HomeMy WebLinkAboutManager's Overview Local Government
GIS Development Guides ~
Manager's Overview : ii~.:i
Needs Assessment ~
Conceptual Design of the GIS i'i~'/
Prepared by:
Erie County Water Authority
National Center for Geographic
Information and Analysis, SUNY at Buffalo
GIS Resource Group, Inc.
Supported by:
New York State Archives and Records Administration
June, 1996
Prepared under the:
Local Government GIS Demonstration Grant
Supported by:
Local Government Records Management Improvement Fund
Local Government Records Services
State Archives and Records Administration
Project Team:
Erie County Water Authority
Mr. Paul Becker, Project Manager
National Center for Geographic Information and Analysis
State University of New York at Buffalo
Dr. Hugh Calkins, Project Director
Ms. Carmelle J. C6t6
Ms. Christina Finneran
GIS Resource Group, Inc.
Mr. Graham Hayes, President
Mr. Thomas Murdoch, Vice-President
For More Information, Contact:
Local Government Technology Services
State Archives And Records Administration
9B38 Cultural Education Center
Albany, New York 12230
Phone: (518) 474-4372
Fax: (518) 473-4941
GIS DEVELOPMENT GUIDE
Volume I
Table of Contents
MANAGER'S OVERVIEW
Introduction ......................................................................................... 1
Geographic Infom~ation Systems: Definitions and Features ......................... 3
Enterprise-wide GIS: The Corporate Database ........................................... 5
Policy Issues in GIS Develoj~ment ............................................................. 6
Management Issues in GIS t~evelopment .................................................... 7
Geographic Information Systems: The Development Cycle ......................... 9
TasksCrxor GIS Development and Use ......................................................... 10
Summary ........................................................................................ 16
References ........................................................................................ 17
Glossary ........................................................................................ 19
Figures
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GIS Development Process ......................................................... 11
Life-Cycle of a GIS Database .................................................... 13
NEEDS ASSESSMENT
Introduction ........................................................................................... 27
Conducting a Needs Assessment .............................................................. 28
Local Government Uses of GIS ................................................................ 29
Data Used by Local Government .............................................................. 32
Documenting GIS Needs .......................................................................... 33
Documenting an Activity-Type Use of the GIS .......................................... 36
Master Data List ..................................................................................... 37
Conducting Interviews ............................................................................ 38
Preparing the Needs Assessment Report .................................................... 40
Summary ............................................................................................... 44
Appendices
A - GIS Application Description Forms ......................................... A-1
B - Full-Page Sample of Master Data List ...................................... B-1
C - Sample GIS Application Description ........................................ C-1
D - Data Flow Diagraming Symbols .............................................. D-1
E - Sample Application Descriptions and Summary Tables ............... E-1
Needs Assessment cont'd
Figures
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GIS Application Descriptions .................................................... 33
Data Flow Diagram Example .................................................... 36
Master Data List ...................................................................... 37
Interviewing and Documenting Needs ........................................ 39
List of GIS Applications ........................................................... 40
Table Summarizing Applications Example .................................. 41
GIS Applications/Data Matrix .................................................... 41
GIS Functions List ................................................................... 42
Compiling Results of Needs Assessment Example ........................ 43
CONCEPTUAL DESIGN OF THE GIS
Part 1 Data Modeling
Introduction ........................................................................................ 46
Nature of Geographic Data ...................................................................... 48
Entity Relationship (E-R) Data Modeling .................................................. 49
Geographic Data Models ......................................................................... 53
Methodology for Modeling ...................................................................... 55
Developing a Spatial Data Model (Entity-Relationship Diagram) ................. 58
Summary of Conceptual Data Modeling ....................................... 59
Part 2: Spatial Data Standards and Metadata Requirements
Metadata Tables ...................................................................................... 61
Additional Reading ................................................................................. 64
Appendix A ...................................................................................... A- 1
Figures
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GIS Development Process ......................................................... 45
Life-Cycle of a GIS Database .................................................... 46
Entities ................................................................................... 49
Example of a Firm's Database ................................................... 50
Example of Simple E-R Diagrams ............................................. 50
Simple E-R Diagrams .................................................. 52
Spatial Relationships ................................................................. 54
Entity Symbol for Spatial Objects .............................................. 56
Entity Relationship Symbols ...................................................... 57
Diagramming a Spatial Relationship ........................................... 58
Example of Entity Relationship Diagram for Local Government...59
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Local Government
GIS Development Guides
Manager's Overview
Prepared by:
Erie County Water Authority
National Center for Geographic
Information and Analysis, SUNY at Buffalo
GIS Resource Group, Inc.
Supported by:
New York State Archives and Records Administration
June, 1996
GIS DEVELOPMENT GUIDE: MANAGER'S OVERVIEW
INTRODUCTION
This guide is the first of a set of technical support documents to assist local governments
in developing a GIS. The set of guides describes procedures and methods for planning the
GIS, evaluating potential data sources, testing available hardware and software and planning for
its acquisition, building the GIS data base, developing GIS applications, and planning for the long
term maintenance of the GIS system and data base. These guides am intended to provide advice
on how best to accomplish the GIS development tasks for all levels of local government - from
large, urbanized counties to small rural towns to special-purpose districts.
Realistically, large comprehensive GISs will be developed by the larger units of government
(counties and cities) individually or, most likely as the leader in a cooperative multi-participant
effort. These would involve the individual operating units within that government and/or the
smaller units of local government within the common land area of the larger leading unit.
Typically, we would expect to see county government taking the lead, but also covering the interest
of all other governmental units within the county. Occasionally, there will be situations where
smaller units of government (town, special purpose district, or limited purpose GIS application)
may have to "go-it-alone" in developing the GIS. These guidelines have been written to mainly
address the first case - a county leading a consortium or cooperative effort. Thus, we would
expect the GIS development team of a county to be the primary user of these guidelines, in the
sense of actually performing the tasks outlined in each document. However, this does not
mean the other participants in a GIS should stop reading these guidelines at this
point. It is critically important for all expected participants in a cooperative GI$
venture to fully understand the development process. If a smaller unit of
government is to reap the benefits of a county-level GI$, they must actively
participate in the planning and development effort.
The procedures are applicable for use in first-time creation of a GIS, for restructuring an on-going
GIS development project, and for the review and further development of an existing GIS. The
subject matter of the guides identifies the necessary tasks in a GIS development program,
describes appropriate methods to accomplish each task and, where applicable, provides examples
and illustrations of documents or other products that result from each task.
The guidelines are designed for use by general-purpose local govemments (city, county, town, or
village), special purpose governments (utilities, school districts, etc.), and by those who provide
assistance to local governments (consultants, academic units, etc.). The guides address the
technical steps required to create a GIS, the management tasks required to ensure
successful development of the GIS, and the policy issues that should be considered for the
effective use of the GIS.
The Role Of Management
Although GIS is often viewed as an arena for the technically sophisticated computer professional,
the development of a successful government-based multi-participant GIS is very dependent on
2 GIS Development Guide
I
proper management participation and supervision. Normal, common-sense management practices
are as necessary in a GIS project as in any other major undertaking. In fact, our experience has
shown that the recommended management actions may be the most critical aspect of the GIS
development process. GIS development is a process of technological innovation and
requires management attention appropriate to this type of activity - active as opposed
to passive management involvement in the project. Historically, much of the disillusions and
disappointment with GIS projects stems not from a failure of the technical components of the GIS
but rather from a lack of understanding of the process of technology innovation and the lack of
realistic expectations of all parties associated with the project (GIS technicians, potential users,
managers, and elected/appointed officials).
Applying The GIS Development Guides By Local Governments In New York
State
The overall procedure contained in the GIS Development Guides is very comprehensive and
can require considerable time, effort and dollars to complete. This raises the questions:
· Does all of this have to be done?
· What level of detail is appropriate?
· How can smaller governments, villages and towns, special purpose districts,
or a single department in a larger jurisdiction, get through this process?
Does everything have to be done? .. level of detail?
Basically, yes. However, the steps in the GIS development process are frequently done in
an iterative manner over an extended time period. Also, the steps are not completely
independent of one another and so some back-and-forth does happen. It is often useful to
make a "first-cut" nm through the entire process, writing down what is already known and
identifying the major questions that need to be answered. The person who will be
managing the development process may be able to do this "first-cut" description in 1 to 2
days. This can be very helpful in getting a feel for the scope of the whole process and
then can be used as a decision tool for continuing. The number of times the process is
conducted, the amount of detail, and the resources needed to complete the study can be
balanced in this way. ff the intended implementation will be limited or small, the
planning effort and documents can be sized accordingly. It is important, however, that
each step be considered and completed at some level. The companion GIS Design
software package that accompanies these guides provides a structure and makes it easy to
record the information developed during the planning process - application descriptions,
data model, data dictionary, metadata, logical database design, and record retention
information.
How can smaller units of local government, such as villages and small towns complete a
GIS Plan?
The best situation for a village, small town, or even a smaller, rural county is to be a
partner with a larger unit of government, a county, regional agency or utility company that
is conducting and/or leading a GIS planning exercise. Participating in a regional GIS
cooperative, or joining an existing one, will provide access to GIS technical expertise and
spatial data created by other agencies. Additionally, if one is a panner in a larger group,
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Manager's Overview 3
the activities directed toward the evaluation and selection of the GIS hardware and
software may not need to be completed. One would simply use the same GIS system in
use by the larger agency or group. Only the activities aimed at de£ming applications (uses)
and identifying the needed data would need to be done by the smaller unit of government.
In such a situation, the larger unit of government assumes the leadership role for the area-
wide GIS and should have the technical expertise to assist the smaller unit. In situations
where a larger effort does not exist, a village or town government may want to look at a
GIS installation in a similar village or town elsewhere in the state. Given the similarities in
local governments within the state, the adoption of the GIS plan of another unit is not
unreasonable. That plan should be carefully reviewed by the intended participants in the
GIS to ensure applicability. After modifying and validating the plan, a schedule for GIS
hardware, software and data acquisition can be prepared consistent with available
resources. If a good plan is prepared, there is no reason data acquisition (the most
expensive part of a GIS) cannot be stretched over a long time period. Significant data
already is available from state and federal agencies at reasonable costs. These data can
form the initial GIS database, with locally generated data added later. A list of state and
federal data sources is contained in the Survey of Available Data Guide.
Content Of This Guide
This guide presents an overview of the GIS development process. This process is presented as
a sequence of steps conducted in a specific order. Each step is important in itself, but
more importantly, information needed to complete subsequent steps is assembled and organized in
each previous step. The underlying philosophy of the entire series of documents is
to concentrate on the GIS data. As well as being the most expensive part of any GIS, the
data must be collected, stored, maintained, and archived under an integrated set of activities in
order to ensure continued availability and utility to the initial users as well as future users,
including the general public. Defining and documenting data elements from their initial def'imtion
in the needs assessment through to proper archiving of the GIS database according to state
requirements is the constant theme of these guidelines.
~ GEOGRAPHIC INFORMATION SYSTEMS: DEFINITIONS AND FEATURES
Basic Definition Of A Geographic Information System (GIS)
A geographic information system (GIS) may be defined as "...a computer-based
information system which attempts to capture, store, manipulate, analyze and display spatially
referenced and associated tabular attribute data, for solving complex research, planning and
management problems" (Fischer and Nijkamp, 1992). GISs have taken advantage of rapid
developments in microprocessor technology over the past several decades to address the special
challenges of storing and analyzing spatial data. Geographers have referred to GISs as
simultaneously providing "...the telescope, the microscope, the computer and the Xerox machine"
for geographic and regional analysis (Abler, 1987).
4 GIS Development Guide
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Unique Features Of A GIS - Why Planning Process Is Needed
GIS belongs to the class of computer systems that require the building of large databases before
they become useful. Unlike many micro-computer applications where a user can begin use after
the pumhase of the hardware and software, the use of a GIS requires that large spatial
databases be created, appropriate hardware and software be purchased,
applications be developed, and all components be installed, integrated and tested
before users can begin to use the GIS. These tasks are large and complex, so large in
fact, as to require substantial planning before any data, hardware or software is acquired. The
focus of the GIS Development Guides is to describe the GIS planning process and to provide
examples of how to accomplish the recommended planning tasks.
History Of Technology Innovations - GIS Is A Technology Innovation
It is useful to note that GIS is, at present, a technological innovation. The adoption of
technological innovations (i.e., the development of a GIS for a local government) is not always a
straightforward process, such as one might expect with the installation of something that is not
new. Several problems are likely to occur such as:
· Staff not fully understanding the technology prior to extensive training
· Development time estimates differing from actual task times
· Greater uncertainty about costs
· A greater likelihood that programmatic changes will be needed during the development
phases, etc.
The significant management point here is that these are normal conditions in the
adoption of a new technology. Management needs to anticipate that such
events will happen, and when they do, take appropriate management actions.
The adoption of computer technology by an organization either GIS or other applications,
introduces fundamental change into the organization in its thinking about data. Prior
information technology allowed data to be collected and related to activities and projects
individually. Organized stores of data were the exception rather than common practice. This led
to duplicate data collection and storage (as in different departments) and to the possibility of
erroneous data existing in one or more locations. One of the goals of computer systems and
database development is to eliminate redundant data collection and storage. The principle is that
data should be collected only once and then accessed by all who need it. Tl~is not only reduces
redundancy; it also allows for more accurate data and a greater understanding of how the same
data is used by multiple departments. The necessary condition for successful computer system and
database development is for different deparlments and agencies to cooperate in the development of
the system. A database becomes an organization-wide resource and is created and managed
according to a set of database principles.
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Manager's Overview 5
ENTERPRISE-WIDE GIS: THE CORPORATE DATABASE
The role of a GIS in a local government setting is more than simply automating a few obvious
tasks for the sake of efficiency. A local government (or several cooperating governments) should
view the GIS project as an opportunity to introduce fundamental change into the
way its business is conducted. As with the adoption of management and executive
information systems in the business world, the adoption of GIS effectively reorganizes the data
and information the government collects, maintains and uses to conduct it affairs. This can, and
arguably should, lead to major changes in the institution, to improve both effectiveness and
efficiency of operations.
A key factor in the success of computer system adoption in the business world is the concept of
the "enterprise" or "corporate" database. As implied by the name, the corporate database is a
single, organization.wide data resource. The advantages of the corporate database are
first, that all users have immediate and easy access to up-to-date information and, secondly that the
construction of the database is done in the most efficient manner possible. Typically, the
corporate database eliminates redundant collection and storage of information and the keeping of
extra copies of data and extra reference lists by individual users. Here, we are recommending the
use of corporate database concept to integrate GIS data for all units of local government
participating in a cooperative GIS program.
An effective corporate database does require cooperation on the part of all users, both for
the collection and entry of data in the database and in developing applications in a shared data
context. This may result in some individual applications or uses being less efficient, however the
overall benefits to the organization can easily outweigh these inefficiencies. Greater emphasis
must, however, be placed on maintaining a high quality of data and services to users, mainly to
offset the perceived loss of control that accompanies sharing an individual's data to another part of
the organization.
The corporate database concept can be used in the governmental situation, for either single units
of government or between several governmental entities in the same region. The benefits
associated with the corporate database can be achieved if governmental units are willing to
cooperate and share a multi-purpose regional GIS database. Such an arrangement has some
technical requirements; however, establishing the corporate database is much more a
question of policy , management cooperation and coordination.
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6 GIS Development Guide
POLICY ISSUES IN GIS DEVELOPMENT
There are several policy issues that need to be addressed early in the GIS planning process:
GIS Project Management
Adequate management attention has already been mentioned in this document. As GIS is still
an evolving new technology, the individuals involved (management, users, GIS staff) may have
very different expectations for the project, some based on general perceptions of computing,
which may or may not be correct. This, along with the long time period for developing the GIS,
makes it very important for substantial involvement of management in the project. Several factors
associated with successful GIS projects are:
· Emphasize advantages of GIS to individual users and entire organization
· Require high level of competency by all participants
· Ensure high level of management commitment from all management levels in the
organization
· Require participation in team building and team participation within & between
departments
· Ensure minimum data quality and access for all users
· Require development team to set realistic expectations
· Minimize time between user needs assessment and availability of useful products.
· Develop positive attitude toward change within organization
· Ensure level of technology is appropriate for intended uses
· Highly visible Pilot Project that is successful
Data Sharing
The sharing of data among government agencies is a virtual necessity for a
successful, long-term GIS. Not even the most affluent jurisdictions will be able to justify "going-
their-own-way" and not taking advantage of what data are available from other sources or not
sharing their database with other governmental units. This, then, raises several questions that must
be considered during the planning oftbe GIS:
· What will be the source for each data item?
· How will sharing be arranged? .. purchase? .. license?., other agreement?
· Who will own the data?
· How will new GIS data be integrated with existing data files (legacy systems)?
· Who will be responsible for updates to the data?
· How will the cost of the data (creation and maintenance) be allocated?
· Who will provide public access to the data?
· Who will be responsible for data archiving and retention? . . of the original? ..of
copies?
These questions do not, at this time, have good answers. Currently, the Freedom of Information
regulations require that all government data be made available to the public at minimal cost (cost of
making a copy of the data). No distinction is made on the basis of the format of the data (eye-
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Manager's Overview 7
readable or digital), the amount of data, or the intended use of data. Thus, the question of sharing
the cost of a GIS database cannot be addressed in general. If data can be obtained free from
another agency, why enter into an agreement to pay for it? The answer is, of course, that the
creating agency will not be able to sustain the GIS database under these circumstances. However,
at this time , the set of state laws and regulations applicable to GIS data are not
adequate to resolve cost issues and to facilitate regional data sharing
cooperatives. New legislation will be required. The New York State Temporary GIS Council
did submit recommendations on these issues to the Legislature in March 1996. Additionally,
the New York State Archives and Records Administration is currently in the process of preparing
record management and retention schedules suitable for GIS data, both in individual agencies and
for shared databases. The New York State Office of Real Property Services has been designated
as the GIS representative on the Governor's Task Force for Information Resource Management.
One of the charges that has been given to the Task Force is to design a cohesive policy for the
coordination of geographic information systems within New York building on the work of the
Temporary GIS Council. Further information should be available in late-1996 that should clarify
the issues associated with arranging for data sharing among governments.
MANAGEMENT ISSUES IN GIS DEVELOPMENT
Expected Benefits From The GIS
Local government need for, and use of, a GIS falls into several categories: maintaining
public records, responding to public inquiries for information, conducting
studies and making recommendations to elected officials (decision-makers), and
managing public facilities and services (utilities, garbage removal,
transportation, etc.). The GIS tasks that meet these uses are:
· Providing regular maps
· Conducting spatial queries and displaying the results
· Conducting complex spatial analyses
Many of these tasks are already done by local government, although by manual means. The GIS
is able to perform these tasks much mom efficiently. Some of the analytical tasks cannot be
performed without a computer due to their size and complexity. In these cases, the GIS improves
local government effectiveness by providing better information to planners and decision-makers.
Benefits from using a GIS fall into the two categories of: efficiency and effectiveness.
Existing manual tasks done more efficiently by the GIS result in a substantial savings of staff
time. In the local government context, the largest savings come from answering citizen inquiries
of many types. Depending on the size of the government, savings using the query function of
a GIS can range from 2 person-years for a smaller town, to 5-8 person years for a large town, to
10 or more person-years for a large county. Estimates of potential time savings can be derived by
measuring the time to respond to a query manually and by GIS and multiplying the difference by
the number of expected queries. This information is usually gathered during the Needs
Assessment. Effectiveness benefits are more difficult to estimate. The GIS may be used to
accomplish several tasks that were not previously done due to their size and complexity (e.g.,
flow analysis in water and sewer systems, traffic analysis, etc.). As these are essentially new
tasks, a comparison between manual and GIS methods is not possible. While not measurable, the
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8 GIS Development Guide
benefits from these applications can be substantial. Generally categorized as better planning,
better or more effective decision-making, these applications support more effective
investment of government resources in physical infrastructure where relatively small performance
improvements can translate into large dollar savings. GIS also provides an effective way to
communicate the problem and solution to the general pubhc and other interested parties
Resources Required To Develop A GIS
Developing a GIS involves investment in five areas: computer hardware,
computer software, geographic data, procedures and trained staff. The acquisition
of the computer hardware and software are often incorrectly viewed as the most expensive activity
in a GIS program. Research, some conducted at the National Center for Geographic Information
and Analysis at SUNY-Buffalo, has demonstrated that developing the geographic database
(which includes some of the procedure and staff costs) can account for 60% to
80% of the GIS development costs. Continuing costs for operation and maintenance are
also dominated by the data costs. Coordination of GIS programs, particularly among several local
government agencies, can minimize the cost of database construction and maintenance, and can
provide for the greatest use of the database, which gives maximum benefits from the investment.
Staffing Requirements For A GIS
Staffing for a GIS is a critical issue. In general, it is not easily feasible to directly expand the
local government staff positions to fill the GIS need. There are three areas where expertise is
needed:
· Management of the GIS project (GIS project manager)
· GIS database skills (usually called a database administrator)
· Application development for database and users (a GIS software analyst)
Initial creation of the GIS database (digitizing) will require an appropriately sized clerical staff,
dependent on the amount of data to be converted. Alternatives to staff expansion are
consultants and data conversion firms. GIS database conversion is a front-end staff need
that can easily be contracted-out (good quality specifications need to be written for this task). If at
all possible, the three functions of GIS manager, GIS software analyst and GIS
database administrator should be fulfilled by staff personnel, either by hiring or by retraining
existing professionals. When necessary, during the start-up phases of GIS development, the GIS
analyst and database administrator functions can be done under consultancy arrangements,
PROVIDED THATA FULL-TIME GIS MANAGER IS AVAILABLE ON STAFF.
The second need is for training of users in general computing, database principles, and GIS use.
These topics are covered in training courses offered by most GIS vendors, and after the
GIS software has been selected, they are the best source for user training.
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Manager's Overview 9
Management Decision Points in the GIS Development Program
The "decision" to develop a GIS is made incrementally. The information needed to determine
the feasibility and desirability of developing a GIS is not available until several of the planning
steps have been completed. The key decision points are:
Decision to investigate GIS for the organization - the initial decision to begin the
process. This is an initial feasibility decision and is based on the likelihood that a GIS
will be useful and effective. It is fairly important to identify the major participants at
this point - both departments within agencies and the group of agencies, particularly
key agencies, the agencies who represent a majority of the uses and who will
contribute most of the data.
Decision to proceed with detailed planning and design of the database - at this time,
the applications, data required, and sources of the data have been identified.
Applications can be prioritized and scheduled and the benefits stream determined.
Also, applications to be tested during the pilot study and the specific questions to be
answered by the pilot study will have been determined. A preliminary decision will
need to be made as to which GIS software will be used to conduct the pilot study.
Decision to acquire the GIS hardware and software - this decision follows the
preparation of the detailed database plan, the pilot study and, if conducted, the
benchmark test. This is the first point in the development process where the costs of
the GIS can reasonably be estimated, the schedule for data conversion developed, and
targets for users to begin use determined.
GEOGRAPHIC INFORMATION SYSTEMS: THE DEVELOPMENT CYCLE
Developing a GIS is more than simply buying the appropriate GIS hardware and software.
The single most demanding part of the GIS development process is building the
database. This task takes the longest time, costs the most money, and requires the most effort in
terms of planning and management. Therefore the GIS development cycle presented here
emphasizes database planning. Most local governments will acquire the GIS hardware and
software from a GIS vendor. Choosing the right GIS for a particular local government involves
matching the GIS needs to the functionality of the commercial GIS. For many agencies,
especially smaller local governments, choosing a GIS will require help from larger, more
experienced agencies, knowledgeable university persons and from qualified consultants. By
completing selected tasks outlined in these guidelines local governments can prepare themselves to
effectively interact and use expertise from these other groups.
The GIS development cycle starts with the needs assessment where the GIS functions
and the geographic data needed are identified. This information is obtained through
interviewing potential GIS users. Subsequently, surveys of available hardware, software and data
are conducted and, based in the information obtained, detailed GIS development plans are
formulated.
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10 GIS Development Guide
It is important to involve potential users in all stages of GIS development. They benefit from
this involvement in several ways:
· Describing their needs to the GIS analysts
· Learning what the GIS will be capable of accomplishing for them
· Understanding the nature of the GIS development cycle - the time involved and the
Costs.
Potential users need to understand that there may be significant time lags between
the first steps of Needs Assessment and the time when the GIS can actually be
used. Mostly, this is due to the size of the database building task, which can take up to several
years in a large jurisdiction.
In addition to understanding that database development takes substantial time, users and
managers need to appreciate that GIS is a new technology and its adoption often involves some
uncertainty that can cause time delays, on-going restructuring the development program, and the
need to resolve unforeseen problems. This set of guideline documents describes the GIS
development process in a way that will minimize problems, time delays, cost overruns, etc.;
however, the occurrence of these situations cannot be completely avoided. The GIS project
team and management simply have to be aware that some unforeseen events will
happen. GIS development must be viewed as a process rather than a distinct project.
Estimating and planning for the cost of the GIS is a somewhat difficult task. First, it is
necessary to recognize that the GIS database will likely be the single most costly item - if a local
government develops all of the data itself from maps, etc., this cost can be as much as 70 - 80 %
of the total system cost. Thus, acquiring digital data from other GIS systems,
government sources or the private sector can be very cost effective. Participating
in, or organizing a regional data sharing cooperative or district, can also lead to reduced data costs.
When planning for the GIS database, long term data maintenance and retention costs
must be estimated as well as the initial start-up costs. Cooperation between agencies
with similar data needs may provide the most effective way to achieve long-term data maintenance,
retention, and archiving.
TASKS FOR GIS DEVELOPMENT AND USE
The GIS development cycle is a set of eleven steps starting with the needs assessment and
ending with on-going use and maintenance of the GIS system. These steps are presented here as a
logical progression with each step being completed prior to the initiation of the next step. While
this view is logical, it is not the way the world always works. Some of the activities in the
process may happen concurrently, may be approached in a iterative manner, or may need to be
restructured depending on the size and character of the local government conducting the study and
the resources available to plan for the GIS. The GIS development cycle is based on the
philosophy that one first decides what the GIS should do and then as a second
activity decides on how the GIS will accomplish each task. Under this philosophy,
the needs are described £zrst, available resources are inventoried second (data, hardware, software,
staff, f'mancial resources, etc.), preliminary designs are created and tested as a third major set of
activities, and lastly the GIS hardware and software are acquired and the database is built.
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Manager's Overview 1 1
ConceptuaJ
Design
Available
Data Survey
H/W & S/W
Sun~ey
end Design
Figure 1 - GIS Development Process
Figure 1 shows the GIS development cycle, which is described in terms of 11 major activities.
Prior to initiating these studies, the responsible staff in local governments should attend
introductory GIS seminars and workshops, GIS conferences, and meetings of specific GIS users'
groups, to obtain a broad overview of what GIS is and how others are using these systems.
The 11 steps of the GIS development cycle are:
1. Needs Assessment
2. Conceptual Design of the GIS
3. Survey of Available Data
4. Survey of GIS Hardware and Software
5. Detailed Database Planning and Design
6. Database Construction
7. Pilot Study/Benchmark Test
8. Acquisition of GIS Hardware and Software
9. GIS System Integration
10. GIS Application Development
11. GIS Use and Maintenance
These tasks are one way of dividing up the entire set of activities that must be accomplished to
build a successful GIS. While there are other ways of expressing and organizing these activities,
this particular structure has been chosen because it emphasizes data development - data definition,
data modeling, data documentation, data capture and storage, and data maintenance and retention.
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1 2 GIS Development Guide
The important point to be made here is not the order or structure of the tasks, but rather that, one
way or another, all of these tasks must be completed to have a successful GIS.
In some situations, different methods may be more appropriate than those presented in these
guides, or a different level of detail may fit the particular situation of a unit of local government.
No matter how simple or complex a given GIS environment is, all of the above tasks should
be completed at an appropriate level of detail. In the specific guides of this set, examples of
different levels of detail will be provided.
The starting point is the needs assessment. It is assumed that the local government has decided
that a GIS may be justified and it is reasonable to expend the resources to further study the
problem. A final assessment of the costs and benefits will not be made until several tasks have
been completed and the nature and size of the resulting GIS can be estimated. In the process
presented here, this final feasibility assessment is made as part of the detailed database planning
and design activity.
Each of the major portions of the development cycle identified and briefly described below is
further described in a subsequent guideline document.
Needs Assessment
The GIS needs assessment is designed to produce two critical pieces of information:
· The list of GIS functions that will be needed
· A master list of geographic data.
These two information sets are extracted from a set of GIS application descriptions, a list of
important data, and a description of management processes. Standard forms are used to document
the results of user interviews. The information gained in the needs assessment activity goes
directly into the Conceptual GIS Design activity.
Conceptual Design of the GIS System
The conceptual design of the GIS system is primarily an exercise in database design. It includes
formal modeling (preparation of a data model) of the intended GIS database and the initial stages
of the database planning activity. Database planning is the single most important
activity in GIS development. It begins with the identification of the needed data and goes on
to cover several other activities collectively termed the data life cycle - identification of data in
the needs assessment, inclusion of the data in the data model, creation of the metadata, collection
and entry of the data into the database, updating and maintenance, and, finally, retention according
to the appropriate record retention schedule (Figure 2). A complete data plan facilitates all phases
of data collection, maintenance and retention and as everything is considered in advance, data
issues do not become major problems that must be addressed after the fact with considerable
difficulty and aggravation. The product of the conceptual design activity is a data model which
rigorously defmes the GIS database and supports the detailed database planning activity.
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Manager's Overview 13
Data Objects Source Documents:
~)~;Pa~°f ~1 tMo a~hail~leed ;da~ata ~ Survey and EvJ~X~uation
and Sources of Available Data
Create ~
,nit~ai I ~laatPa a~cdn vT ea ~r .~ ~ loanr
Metadata ]
GIS Database
~;~gMGa~ance
Archives
Database Backups
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Figure 2 - Life Cycle of a GIS Database
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1 4 GIS Development Guide
The conceptual design of the GIS also includes identification of the basic GIS architecture (type
of hardware and GIS software), estimates of usage (derived from the Needs Assessment), and
scoping the size of the GIS system. All of this is done with reference to the existing data
processing environments (legacy systems) that must interface with the GIS. This guideline also
includes a section on metadata and data standards.
Survey Of Available Data
A survey of available data can commence once needed data have been identified in the
Needs Assessment. This task will inventory and document mapped, tabular and digital data
within the local government as well as data available from other sources, such as federal, state, or
other local governments and private sector organizations. The entries in this inventory may
include other GIS systems within the local area from which some of the needed data may be
obtained. If there exists an organized data sharing cooperative or other mechanism for
government data sharing, it should be investigated at this time. There also exists the possibility
that one or more of the commercial GIS database developers may be able to supply some of the
needed data and should therefore be investigated. The documentation prepared at this point will be
sufficient to evaluate each potential data source for use in the GIS. Information collected at this
point will also form part of the metadata for the resulting GIS database.
Survey Of Available GIS Hardware And Software
Almost all local government GIS programs will rely on commercially available GIS software.
As a result, a survey of the available GIS systems needs to be conducted. During this activity,
the GIS functionality of each commercial GIS system can be documentext for later evaluation.
Detailed Database Design And Planning
The detailed database planning and design task includes the following activities: developing
a logical or physical database design based on the data model prepared earlier, evaluating the
potential data sources, estimating the quantities of geographic data, estimating the cost of building
the GIS database and preparing the data conversion plan. Concurrent with the detailed planning
for the database, pilot studies and/or benchmark testing that are desired can be executed.
Information gained from these studies and tests will be needed to estimate the size of the
equipment (disk space, main memory etc.) and to determine how much application development
will be necessary. Subsequently, plans for staffing, staff training, equipment acquisition and
installation, and user training must be completed. After the preparation of all these plans, the
entire cost of the GIS will be known and the final feasibility assessment can be made.
Pilot Study And Benchmark Tests
Pilot studies and benchmark tests are intended to demonstrate the functionality of the GIS software
- simply put, what the commercial GIS from the vendor can do. These tests are useful to
demonstrate to potential users and management what the GIS will do for them. Also, performance
data of the GIS system can be determined.
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Manager's Overview 15
GIS Database Construction
Database construction (sometimes referred to as "database conversion") is the process of
building the digital database from the source data - maps and tabular files. This
process would have been planned during the previous activity and the main emphasis here is
management of the activity and quality assurance/quality control of the converted data. The
conversion process is often "contracted-out" and involves large quantities of source maps and
documents. Close and effective management is the critical factor in successful data conversion.
GIS System Integration
Unlike many other computer applications, a GIS is not a "plug and play" type system. The
several components of a GIS must be acquired according to well documented specifications. The
database must be created in a careful and organized manner. Once all the individual
components have been acquired, they must be integrated and tested. Users must be introduced to
the system, trained as necessary, and provided with adequate assistance to begin use of the GIS.
Parts of the GIS which may appear to work fine individually may not work properly when
put together. The GIS system staff must resolve all the problems before users can access the GIS.
GIS Application Development
"Application" is a general term covering all things that "go on" in a GIS. First,
there are "database applications." These are all the functions needed to create, edit, build, and
maintain the database, and are usually carded out by the GIS systems staff. Some users may have
responsibility for updating selected parts of the GIS database, however the entire database should
be under the control of a "database administrator." Other applications are temaed "user
applications." Contemporary GISs provide many simple applications as part of the initial
software package (e.g., map display, query, etc.). More complex applications, or ones
unique to a particular user, must be developed using a macro-programming language.
Most GISs have a macro-programming language for this purpose (e.g., Arc Macro Language
(AML) in ARC/INFOTM. and Avenue in ArcViewm). The applications needing development by
the GIS systems staff will have been described during the Needs Assessment on the GIS
Application forms.
GIS System Use And Maintenance
After having described the rather large task of creating a GIS, we can now say that use
and maintenance of the GIS and its database will likely require as much attention as was needed to
initially build it. Most GIS databases are very dynamic, changing almost daily, and users will
immediately think of additional applications that they would like to have developed. Formal
procedures for all the maintenance and updating activities need to be created and followed by the
GIS system staff and by all users to ensure continued successful operation of the GIS.
1 6 GIS Development Guide
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SUMMARY
This document has presented an overview of the GIS development process, with an emphasis on
data and database issues. All of the tasks and issues identified in this document will be described
in detail in the remaining eleven guidelines of this series. The procedures are presented as
"guides," and not as a "cookbook recipe" which must be rigorously followed. Each of the major
tasks in the GIS development process and the information generated within the task should be
addressed in any specific project. The methods and forms used in this series can be used, or
alternatives can be developed, as appropriate to the situation. The one matter to always keep in
mind is that the GIS plan is a document to communicate user needs to a GI$
analyst. The components of the plan must contain:
· Descriptions of applications that are understandable to the user
· A logical translation of user requirements to system specifications
· Detailed specification suitable for system development
Following the recommendations in these guidelines cannot, unfortunately, guarantee success.
Many of the factors, outside the control of the GIS development team, will affect the ultimate
success of the GIS - success being defined as use of the GIS by satisfied users. However, the
authors of these guidelines believe that attempting to develop a GIS without following these, or
similar procedures, substantially raises the probability of an unsuccessful GIS project - either one
that is not useful or one that substantially exceeds both cost and development time estimates.
Finally, although presented here as an independent activity, GIS development must recognize and
interface with other computer systems in local government, such as Egl 1, police and fire dispatch,
facilities management systems, etc.. The GIS must not be viewed as independent of the other
systems, but integrated with them, no matter how difficult, to form a true corporate database
for local government.
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Manager's Overview 17
REFERENCES
1) Fischer, Manfred M. and Nijkamp, Peter, "Geographic Information System, Spatial Modeling,
and Policy Evaluation," Berlin & New York: Springer-Verlag, 1993, pg 42.
2) Abler, R.F., 1987, "The National Science Foundation National Center for Geographic
Information and Analysis" International Journal of Geographical Information Systems, 1, no. 4,
303-326.
SUGGESTED READINGS
1. Antenucci, John C., et. al., Geographic Information Systems: A Guide to the
Technology, New York: Van Nostrand Reinhold, 1991 (ISBN 0-442-00756-6)
2. Aronoff, Stan, Geographic Information Systems: A Management Perspective,
Ottawa: WDL Publications, 1989 (ISBN 0-921804-00-8)
3. Burrough, P.A., Principles of Geographical Information Systems for Land
Resources Assessment, Oxford: Oxford University Press, 19865. (ISBN 0-19-854563-0);
ISBN 0-19-854592-4 paperback).
4. Huxhold, William E., An Introduction to Urban Geographic Information Systems,
Oxford: Oxford University Press, 1991 (ISBN 0-19-506534-4)
5. Korte, George B., A Practloner's Guide: The GIS Book, Sante Fe: OnWord Press,
1992 (ISBM 0-934605-73-4)
6. Laurini, Robert and Derek Thompson, Fundamentals of Spatial Information Systems,
London: Academic Press Limited (ISBN: 0-12-438380-7)
7. Montgomery, Glenn E., and Harold C. Schuck, GIS Data Conversion Handbook, Fort
Collins: GIS World, Inc. (ISBN 0-9625063-4-6)
GIS INFORMATION SOURCES
Scholarly journals
There are a number of scholarly journals that deal with GIS. These are published on an on-going
basis.
Cartographica - Contact: Canadian Cartographic Association
Cartography and Geographic Information Systems - Contact: American Cartographic
Association
International Journal of Geographical Information Systems - Contact: Keith Clark at
CUNY Hunter College, New York City
URISA Journal - Contact: Urban and Regional Information Systems Association
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1 8 GIS Development Guide
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Trade magazines
There are a number of trade magazines that are
focused on GIS. They are:
GIS World
GIS World Inc.
155 E. Boardwalk Drive
Suite 250, Fort Collins, CO 80525.
Phone: 303-223-4848
Fax: 303-223-5700
Intemet: info@gisworld.com
Business Geographics
GIS World, Inc.
155 E. Boardwalk Drive, Suite 250
Fort Collins, CO 80525.
Phone: 303-2234848
Fax: 303-223-5700.
Intemet: info@gisworld.com.
Geo Info Systems
Advanstar Communications
859 Williamette St.
Eugene, OR., 97401-6806
Phone: 541-343-1200
Fax: 541-344-3514
Intemet:geoinfomag @ aol.com
WWW site:http://www.advanstar.comJgeo/gis
GPS World
Advanstar Communications
859 Williamette St.
Eugene, OR., 97401-6806
Phone: 541-343-1200
Fax: 541-344-3514
Intemet:geoinfomag @ aol.com
WWWsite:http://www.advanstar.com/geo/gis
Conference Proceedings
American Congress on Surveying and
Mapping (ACSM)
5410 Grosvenor Lane
Bethesda, MD, 20814
Phone: 301-493-0200
Fax: 301-493-8245
American Society for Photogrammetry
and Remote Sensing
(ASPRS) & (GIS/LIS)
5410 Grosvenor Lane
Bethesda, MD, 20814
Phone: 301-493-0290
Fax: 301-493-0208
Association of American Geographers
(AAG)
1710 Sixteenth St. N.W.
Washington D.C., 20009-3198
Phone: 202-234-1450
Fax: 202-234-2744
Automated Mapping/Facility
Management International (AM/FM
International)
14456 East Evans Ave.
Aurora, CO, 80014
Phone: 303-337-0513
Fax: 303-337-1001
Canadian Association of Geographers
(CAG)
Burnside Hall, McGill University
Rue Sherbrooke St. W
Montreal, Quebec H3A 2K6
Phone: 514-398-4946
Fax: 514-398-7437
Canadian Institute of Geomatics (CIG)
206-1750 me Courtwood Crescent
Ottawa, Ontario, K2C 2B5
Phone: 613-224-9851
Fax: 613-224-9577
Urban And Regional Information
Systems Association (URISA)
900 Second St. N.E., Suite 304
Washington, D.C. 20002
Phone: 202-289-1685
Fax: 202-842-1850
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Glossary
Accuracy - Degree of conformity with a standard, or the
relates to the quality of a result. If accuracy is relative, the
position of a point is defined in relation to another point.
It is less expensive to build a GIS in the context of relative
accuracy. If accuracy is absolute, the position of a point is
defined by a coordinate system. Building a GIS in the
context of absolute accuracy requites use of the global
positioning system.
Accuracy Requirement - statement of how precise the
desired results must be to support a particular application.
Adjoining Sheets - Maps that ate adjacent to one
another at the comers and on one or more sides.
Aerial - Relating to the air atmosphere, being applicable
in a descriptive sense to anything in space above the
ground and within the atmosphere.
Aerial Photography - The method of taking
photographs from an aerial platform (aircraft). (1.) Vertical
photography, some times called orthophotography (see
entry) is used for photogrammetric mapping and requires a
high degree of accuracy. (2.) Oblique photography is used
for general information, sometimes to verify certain
attributes, but does not provide accurate measurements for
photogrammetric mapping.
Aerial Survey - A survey utilizing aerial photography or
from remote sensing technology using other bands of the
electromagnetic spectrum such as infrared, gamma or
ultraviolet.
Algorithm - A set of instructions; ordered mathematical
steps for solving a problem like the instructions in a
computer program.
Alignment - Relates to survey data transposed to maps.
The correct position of a line or feature in relation to other
lines or features. Also the correct placement of points
along a straight line.
Alphanumeric - A combination of alphabetic letters,
numbers and or special characters. A mailing address is an
alphanumeric listing.
Analog Data - Data represented in a continuous form,
not ~eadable by a computer.
Area - level of spatial measurement referring to a two-
dimensional defined space; for example, a polygon on the
earth as projected onto a horizontal plane.
Attribute - 1. A numeric, text, or image data field in a
relational data base table that describes a spatial feature
such as a point, tine, node, area or cell. 2. A characteristic
of a geographic feature described by numbers or characters,
typically stored in tabular format, and linked to the feature
by an identifier. For example, attributes of a well
(represented by a point) might include depth, pump type,
location, and gallons per minute.
Manager's Overview 19
AM/FM - Automated mapping/facilities management. A
GIS designed primarily for engineering and ulility
purposes, AM/FM is a system that manages databases
related to spatially distributed facilities.
Base Data - set of information that provides a baseline
orientation for another layer of primary focus, e.g., roads,
streams, and other data typically found on USGS
topographic and/or planimewic maps.
Base Line - A surveyed line established with more than
usual care upon which surveys are based.
Base Map - A map showing planimetric, topographic,
geological, political, and/or cadastral information that
may appear in many different types of maps. The base map
information is drawn with other types of changing
thematic information. Base map information may be as
simple as major political boundaries, major hydrographic
data, or major roads. The changing thematic information
may be bus routes, population distribution, or caribou
migration routes.
Base Station - a GPS receiver on a known location that
may broadcast and/or collect correction information for
GPS receivers on unknown locations.
Bench Mark - A relatively permanent point whose
elevation above or below an adopted datum is known.
Beta Test - Hardware or software testing performed by
users in a normal operating environment; follows alpha
testing, which is generally done in the developer's facility.
Bezier - (computer graphics) A carve generated by a
mathematical formula in CAD (see entry) programs that
maintains continuity with other Bezier curves.
Binary - The fundamental principal behind digital
computers. Binary means two, computer input is converted
into binary numbers made up of O and 1 (see bit).
BIT: (computers) a binary digit with a value of either 1 or
0.
Block (Tax) - A group of municipal tax lots that can be
isolated from other parcels by a boundary, usually a
roadway, waterway or properly labeled lot line.
Boundary Line - A line along which two areas meet. In
specific cases, the word "boundary" is sometimes omitmd,
as in "state line", sometimes the word "line" is omitted, as
in "thtemational boundary", "county boundary", etc. The
term "boundary line" is usually applied to boundaries
between political territories, as "state boundary line",
between two states. A boundary line between privately
owned parcels of land is termed a property line by
preference, or if a line of the United States public land
surveys, is given the particular designation of that survey
system, as section line, township line, etc.
BPS - Bits per second, the speed of data transfer.
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20 GIS Development Guide
Buffer A zone of a given distance around a physical entity
such as a point~ line, or polygon.
CAD/CADD - (Computers) Computer-Aided Design/
Computer-Aided Design and Drafting. Any system for
Computer-Aided rather than manual drafting and design.
Displays data spatially, on a predefined coordinate grid
system, allowing data from different sources to be
connected and referenced by location. Speeds conventional
map development process by 1. permitting replication of
shapes, floor plans, etc. from an electric hbrary rather than
requiring every component to be drawn from scratch. 2.
Plotters and terminal screens are faster and more accurate
than manual diafting. 3. Portions of drawings can be edited,
enlarged, etc. quickly. 4. Related information can be stored
in files and added to drawings in layers.
CAD - (Communication) Computer-Aided Dispatching.
Used with emergency vehicles, CAD can be very
sophisticated. Online maps of a city can display
emergency vehicles as moving dots on the map, their
status (enroute to an emergency, awaiting a call, call
completed, returning to base, etc.) indicated by different
colors. (The acronym for computer-aided dispatch is
sometimes confused with computer-aided design.)
Cadastre - a record of interests in land, encompassing
both the nature and extent of interests. Generally, this
means maps and other descriptions of land parcels as well
as the identification of who owns certain legal rights to the
land (such as ownership, liens, easements, mortgages, and
other legal interests). Cadas~ral information often includes
other descriptive information about land parcels.
Cadastral - Relating to the value, extent and ownership
of land for tax purposes. Cadaslral maps describe and record
ownership. Also called property map.
Cadnstral Survey - A survey relating to land boundaries
and subdivisions, made to create units suitable for transfer
or to define the limitations to title. Derived from
"cadas~e", and meaning register of the real property of a
political subdivision with details of area, ownership, and
value. The term cadas~al survey is now used to designate
the surveys for the identification and resurveys for the
restoration of property lines; the term can also be applied
properly to corresponding surveys outside the pubhc lands,
although such surveys are usually termed land surveys
through preference. See also boundary, survey.
Cartographic (Planimetric) Features - Objects like
trees or buildings shown on a map or chart.
Cartography - The technology of mapping or charting
features of Earth's topography.
Centroid - The "center of gravity" or mathematically
exact center of an irregular shaped polygon; often given as
an x, y coordinate of a parcel of land.
Clearinghouse - a physical repository structure used to
accumulate and disseminate digital data and information
concerning that data. In the GIS context a clearinghouse
can contain all or a portion of spatial, metadata and
informational data.
Client - A software application that works on your behalf
to extract some service from a server somewhere on the
network. Basic idea, think of your telephone as a client
and the telephone company as a server.
COGO - Acronym for Coordinate Geometry achieved via a
computer program.
Computer-aided Design or Drafting (CAD) - A
group of computer software packages for creating graphic
documents.
Control Point - A point in a network, identifiable in
data or a photograph, with a given horizontal position and
a known surface elevation. It is correlated with data in date
set or photograph.
Contour - An imaginary outline of points on the ground
which are at the same altitude relative to mean sea level.
Contour Line - A hue on a map or chart that connects
to points which are at the same elevation.
Contour Map - A map that defines topography
(hypsography) by interpreting contour lines as relief.
Control - Also called ground control. A system of survey
marks or objects called control points that have
established positions and/or elevations verified by ground
survey. The marks, or con~xol points, serve as a reference
correlating other data such as contour lines (see entry)
determined from aerial surveys.
Conversion - 1. The translation of data from one format
to another (e.g., TIGER to DXF; a map to digital files).S 2.
Data conversion when transferring data from one system to
another (E.g., SUN to IBM).s
Coordinate - The position of point is space in respect to
a Cartesian coordinate system (x, y and/or z values). In
GIS, a coordinate often represents locations on the earth's
surface relative to other locations.
Coordinate System - The system used to measure
horizontal and vertical distances on a planimetric map. In a
GIS, it is the system whose units and characteristics are
defined by a map projection. A common coordinate system
is used to spatially register geographic data for the same
area. See map projection
CRT - Cathode Ray Tube. A computer screen or monitor.
CIG - Center for Technology in Government
Data Capture - series of operations required to encode
data in a computer-readable digital form (digitizing,
scanning, etc.)
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Manager's Overview 21
Data Dictionary - description of the information
contained in a data base, e.g., format, definition, structure,
and usage. It typically describes and defines the data
elements of the data base and their interrelationships
within the larger context of the date base.
Data Element - specific item of information appearing
in a set of data, e.g. well site locations.
Data Model 1. A generalized, user-defined view of the
data related to applications. 2. A formal method for
arranging data to mimic the behavior of the real world
entities they represent. Fully devuloped data models
describe data types, integrity rules for the data types, and
operations on the data types. Some data models are
triangulated irregular networks, images, and georelational
or relational models for tabular data.
Data Quality - refers to the degree of excellence
exhibited by the data in relation to the porlxayal of the
actual phenomena
Data Sets - a collection of values that all pertain to a
single subject.
Data Standardization - the process of achieving
agreement on data definitions, representation, and
structures to which all data layers and elements in an
organization must conform.
Data Structure - organization of data, particularly the
reference linkages among data elements.
Database -usually a computerized ftc or series of fries of
information, maps, diagrams, listings, location records,
abstracts, or references on a particular subject or subjects
organized by data sets and governed by a scheme of
organization. "Hierarchical" and relational" define two
popular structural schemes in use in a GIS. For example, a
GIS database includes data about the spatial location and
shape of geographic entities as well as their attributes.
Database Management System (DBMS) - 1. The
software for managing and manipulating the whole GIS
including the graphic and tabular data. 2. Often used to
describe the software for managing (e.g., input, verify,
store, retrieve, query, and manipulate) the tabular
information. Many G1Ss use a DBMS made by another
software vendor, and the GIS interfaces with that software.
Datum - a mathematical reference framework for geodetic
coordinates defined by the latitude and longitude of an
initial point, the azimuth of a line from this point, and the
parameters of the
ellipsoid upon which the initial point is located.
DEC - Department of Environmental Conservation
Differential Correction - the method (usually done
through pest processing) of using two GPS receivers, one
on a known location and one on an unknown location,
using information from the one on the known location to
correct the position of the unknown location.
Digital Accuracy - refers to the accuracy of digital
spatial data capture.
Digital Elevation Model (DEM) - a file with terrain
elevations recorded at the intersections of a fmc grid and
organized by quadrangle to be the digital equivalent of the
elevation data on a topographic base map.
Digital Data - a form of representation in which distinct
objects, or digits, are used to stand for something in the
real world--temperature or time--so that counting and other
operations can be performed precisely. Data represented
digitally can be manipulated to produce a calculation, a
sort, or some other computation. In digital electronic
computers, two electrical states correspond to the Is and Os
of binary numbers, which are manipulated by computer
programs.
Digital Exchange Format (DXF) 1. ASCII text files
defmed by Autodesk, Inc. (Sausalito, CA) at first for CAD,
now showing up in third-party GIS software . 5 2. An
intermediate file format for exchanging data from one
software package to another, neither of which has a direct
translation for the other but where both can read and
convert DXF data files into their format. This often saves
time and preserves accuracy of the data by not reautomating
the original.
Digital Line Graph (DLG) 1. In reference to data, the
geographic and tabular data fries obtained from the USGS
for exchange of cartographic and associated tabular date
fries. Many non-DLG data may be formatted in DLG format.
2. In reference to data, the formal standards developed and
pobhshed by the USGS for exchange of cartographic and
associated tabular data fries. Many non-DLG data may be
format~l in DLG format.
Digital Map - A machine-readable representation of a
geographic phenomenon stored for display or analysis by a
digital computer; contrast with analog map.
Digital Orthophoto - A geographically correct digital
image with the same accuracy as a vector digital map, but
preserving the information content of the original
photography.
Digital Orthophoto Quarter-Quad (DOQ)- a 3.75
minute square distortion free image of the surface of the
earth. The imagery has been geographically and
photographically rectified to remove all distortion, and
meet requirements of the USGS.
Digital Terrain Model (DTM) - A computer graphics
software technique for converting point elevation data into
a terrain model displaced as a contour map, sometimes as a
three-dimensinnal "hill and valley" grid view of the ground
surface.
Digitize - A means of converting or encoding map data
that are represented in analog form into digital information
of x and y coordinates.
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22 GIS Development Guide
Digitized Terrain Data - Transposed elevation
information from maps or photographs to X-Y-Z digital
coordinates for storage on magnetic media.
Digitizer - A device used to capture planar coordinate
data, usually as x and y coordinates, from existing
analogmaps for digital use within a computerized program
such as a GIS; Also called a digitizing table.
Digitizing - refers to the process of manually converting
an analog image or map or other graphic overlay into
numerical format for use by a computer with the use of a
digitizing table or tablet and tracing the input data with a
cursor (see also scanning).
DIME - Dual Independent Map Encoding Provides vector
data such as st~ets to census data addresses. Superseded by
Topologically Integrated Geographic Encoding and
Referencing (see TIGER).
DIME File - A geographic base file produced by the U.S.
Census Bureau with Dual Independent Map Encoding. Now
being superseded by TIGER files (see below).
DLG - See Digital Line Graph
DOB - Division of the Budget
DOQ - See Digital Orthophoto Quarter-quad
DOT - Department of Transportation
DTF - Department of Taxation and Finance
Edge Match - An editing procedure to ensure that all
features crossing adjacent map sheets have the same edge
locations, attribute descriptions, and feature classes.
Federal Information Processing Standards
(FIPS) - official source within the federal government for
information processing standards. They were developed by
the Institute for Computer Sciences and Technology, at the
National Institute of Standards and Technology (NIST),
formerly the National Bureau of Standards.
Federal Geographic Data Committee (FGDC)
established by the Federal Office of Management and
Budget, is responsible for the coordination of
development, use, sharing, and dissemination of
surveying, mapping, and related spatial data.
Fifth Generation Computer - A computer designed
for applications of artificial intelligence (Al). Some
elements of spatial data management, especially the CADD
output side, are beginning to integrate A1 computing.
FOIL - Freedom of Information Law
Format - 1. The pattern in which data are systematically
arranged for use on a computer. 2. A file format is the
specific design of how information is organized in the file.
For example, DLG, DEM, and TIGER are geographic data
sets in particular formats that are available for many parts
of the United States 6
File Transfer Protocol (FTP) - a standard protocol
that defines how to transfer files from one computer to
another.
Fortran - A high-level programming language and
compiler originally designed to express math formulas.
Developed in 1954 by IBM it is still the most widely used
language for scientific and engineering programming.
GBF/DIME - See Geographic base file/dual independent
map encoding
Geocode - The process of identifying a location as one or
more x, y coordinates from another location description
such as an address. For example, an address for a student can
be matched against a TIGER street network to locate the
student's home.
Geodetic Monumentation - a permanent structure that
marks the location of a point taking into account the
earth's curvature.
Geographic - Pertains to the study of the Earth and the
locations of living things, humans and their effects.
Geographic Base File/dual Independent Map
Encoding (GBF/DIME) - A data exchange format
developed by the US Census Bureau to convey iniormahnn
about block-face/street address ranges related to 1980
census tracts. These files provide a schematic map of a
city's streets, address ranges, and geostatistical codes
relating to the Census Bureau's tabular statistical data. See
also TIGER, created for the 1990 census.
Geographic Database - Efficiently stored and
organized spatial data and possibly related descriptive data.
Geographic Information Retrieval and Analysis
(GIRAS) - Data files from the US Geological survey.
GIRAS files contain information for areas in the
continental United States, including athSbutes for land use,
land cover, political units, hydrologic units, census and
county subdivisions, federal land ownership, and state land
ownership. These data sets are available to the public in
both analog and digital form.
Geographic Information System (GIS) - A n
organized collection of computer hardware, software,
geographic data, and personnel designed tu efficiently
capture, store, update, manipulate, analyze, and display all
forms of geographically referenced information. Certain
complex spatial operations are possible with a GIS that
would be very difficult, time-consuming, or impractical
otherwise.
Geographic Object - A user-defined geographic
phenomenon that can be modeled or represented using
geographic data sets. Examples include streets, sewer lines,
manhole covers, accidents, lot lines, and parcels.
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Manager's Overview 23
Geographical Resource Analysis Support
System (GRASS) - 1. A public-domain raster GIS
modeling product of the US Army Corps of Engineers
Construction Engineering Research Laboratory. 2. A raster
data format that can be used as an exchange format between
two GISs.
Georectify - the process of referencing points on an
image to the real world coordinates.
Georefereuce - To establish the relationship between
page coordinates on a paper map or manuscript and known
real-world coordinates
Geospatial - a term used to describe a class of data that
has a geographic or spatial nature.
Geostationary Satellite: An earth satellite that
remains in fixed position in sync with the earth's rotation.
GIS - Geographic information system. A computer system
of hardware and software that integrates graphics with
databases and allows for display, analysis, and modeling.
Grid-Cell Data - Grid-cell data entry places a uniform
grid over a map area, and the area within the cell is labeled
with one attribute or characteristic, such as elevation
averaged over all points. Grid cells can be layered with
differing types of information.
Global Positioning System (GPS) - a system
developed by the U.S. Department of Defense based on 24
satellites orbiting the Earth. Inexpensive GPS receivers
can accurately determine ones position on the Earth's
surface.
Ground Truth - Information collected from a survey area
as remote sensing data is being collected from the same
area (see control).
Hierarchical - A way of classifying data, starting with
the general and going to specific labels.
Hydrography - Topography pertaining to water and
drainage feature.
Hypsography - 1 ) The science or art of describing
elevations of land surfaces with reference to a datum,
usually sea level. 2) That part of topography dealing with
relief or elevation of terrain.
Image - A graphic representation or description of an
object that is typically produced by an optical or electronic
device. Common examples include remotely sensed data
such as satellite data, scanned data, and photographs. An
image is stored as a raster data set of binary or integer
values representing the intensity of reflected lighL heat, or
another range of values on the electromagnetic speclrum.
Remotely sensed images are digital representations of the
earth.
Imagery - a two dimensional digital representation of the
earth's surface. Examples are a digital aerial photograph, a
satellite scene, or an akburne radar scan.
Index - A specialized lookup table or structure within a
database and used by an RDBMS or GIS to speed searches
for tabular or geographic data.
Infrastructure - The fabric of human improvements to
natural settings that permits a community, neighborhood,
town, city metropolis, region, state, etc., to function.
Initial Graphics Exchange Specification (IGES)
An interim standard format for exchanging graphics
Polygon data among computer systems.'
lnternet - a system of linked computer networks,
worldwide in scope, that facilitates data communication
services such as remote login, I'de transfer, electronic mail,
and newsgroups. The Internet is a way of connecting
existing computer networks that greatly extends the reach
of each participating system.
Internet Protocol (IP) - the most important of the
protocols on which the Internet is based. It allows a packet
to traverse multiple networks on the way to its final
destination.
Interpolate - Applied to logical contouring by
determining vertical distances between given spot
elevations.
IT - Information Technology
Land Information System (LIS) - the sum of ali the
elements that systematically make information about land
available to users including: the data, products, services,
the operating procedures, eqnipmenL software, and people.
Land Information System (LIS) - NJ State 45:8-
28(e) - Any computer coded spatial database designed for
multi-purpose public use developed from or based on
property boundaries.
Latitude - The north-south measurement parallel to the
equator.
Imyer- A logical set of thematic data, usually organized
by subject matter.
Layers - refers to the various "overlays" of data each of
which normally deals with one thematic topic. These
overlays are registered to each other by the common
coordinate system of the database.
Longitude - The angular distance, measured in degrees,
cast or west from the Greenwich meridian, or by the
difference in time between two reference meridians on a
globe or sphere.
Lot Number - A numerical parcel designation, that when
combined with a block number is unique to a single parcel
of land within a given municipality.
Manual Digitizing - Conversion of an analog
measurement into a digital form by using a manual device
such as a calculator.
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24 GIS Development Guide
Map - A representation of a portion of the earth, usually
drawn on a fiat surface. (From Latin mappa, a napkin, sheet
or cloth upon which maps were drawn.)
Map Projection - A mathematical model for converting
locations on the earth's surface from spherical to planar
coordinates, allowing flat maps to depict three dimensional
features. Some map projections preserve the integrity of
shape; others preserve accuracy of area, distance, or
direction.
Map Units - The coordinate units in which the
geographic data are stored, such as inches, feet, or meters
or degrees, minutes and seconds.
Metadata - data describing a GIS database or data set
including, but not limited to, a description of a data transfer
mediums, format, and contents, source lineage data, and
any other applicable data processing algorithms or
procedures.
NCGIA - National Center for Geographic Information
Analysis
Network Analysis - Addresses relationships between
locations on a network. Used to calculate optimal routes,
and optimal locations for facilities.
NSGIC - National States Geographic Information Council
NSDI - National Spatial Data Inh'astructure
OPRHP - Office of Parks, Recreation and Historical
Preservation
ORPS - Office of Real Propo~ty Services
Orthophoto - A photograph of the earth's surface in
which geographic distortion has been removed.
Overlay - A layer of data representing one aspect of
related information.
Parcel - Generaily refers to a piece of land that can be
designated by number.
Photogrammetry The system of gathering
information about physical objects through aerial
photography and satellite imagery.
Plane-Coordinate System A system for determining
location in which two groups of straight lines intersect at
right angles and have as a point of origin a selected
perpendicular intersection.
Planimetric Map - A map which presents the horizontal
positions only for the features represented; distinguished
from a topographic map by the omission of relief in
measurable form. The natural features usually shown on a
planimetric map include rivers, lakes and seas; mountains,
valleys and plains; and forests, prairies, marshes and
deserts. The culture features include cities, farms,
transportation routes and public-utility facilities; and
political and private boundary lines. A planimetric map
intended for special use may present only those features
which are essential to the purpose to be served.
Plat: A scale diagram void of cultural, drainage and relief
features, showing only land boundaries and subdivisions
together with data essential to its legal description.
Plotter - Equipment that can plot a graphic file using
multiple line weights and colors. Types available today
axe: pen, laser, and electrostatic plotters.
Point Data - level of spatial definition referring to an
object that has no dimension, e.g., well or weather station.
Points - Items such as oil wells, utility poles, etc.
Specific objects with exact location noted.
Polygon - A vector representation of an enclosed region,
described by a sequential list of vertices or mathematical
functions.
Positional Accuracy - term used in evaluating the
overall reliability of the positions of cartographic features
relative to their true position.
Precision - refers to the quality of the operation by
which the result is obtained, as distinguished from
accuracy.
Protocol - a definition for how computers will perform
when talking to each other. Protocol definitions range
from how bits are placed on a wire to the format of an
electronic mail message. Standard protocols allow
computers from different manufacturers to communicate;
the computers can use completely different software,
providing that the programs running on both ends agree on
what the data means.
Quadrangle - A four-sided region, usually bounded by a
pair of meridians and a pair of parallels.
Quality Control - process of taking steps to ensure the
quality of data or operations is in keeping with standards
set for the system.
Raster - A grid-type data format used to interpret gray-
scale photographs and satellite imagery. Imagery is stored
as dots or pixels, each with a different shade or density.
Raster Data- Machine-readable data that represent
values usually stored for maps or images and organized
sequentially by rows and columns. Each "cell" must be
rectangular but not necessarily square, as with grid data.
RDBMS - See relational database management systems.
Rectified - referencing points, lines, and/or features of
two dimensional images to real world geographic
coordinates, to correct distortion in the image.
Rectify - The process by which an image or grid is
converted from image coordinates to real-world
coordinates. Rectification typically involves rotation and
scaling of grid ceils, and thus requires resampling of
values.
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Manager's Overview 25
Registration - the procedure used to bring two maps or
data layers into concurrence via known ground location
control points or the procedure of bringing a map or data
layers into concttrrence with the earth's surface.
Relational Database Management System
(RDBMS) - A database management system with the
ability to access date organized in tebular fries that may be
related together by common fteld (item). An RDBMS has
the capability to recombine the data items from different
fries, thus providing powerful tools for data usage.
Remote Sensing - Recording imagery or data and
information from a distance. Photography is a form of
remote sensing. Satellites provide a remote sensing
platform for developing geology and soils analysis with
sensors sensitive to various bands of the electromagnetic
spectrum.
Resolution - I. The accuracy at which the location and
shape of map features can be depicted for a given map scale.
For example, at a map scale of I:63,360 (1 inch=l mile), it
is difficult to represent areas smaller than 1/I0 of a mile
wide or 1/10 of a mile in length because they are only 1/1
O-inch wide or long on the map. In a larger scale map, there
is less reduction, so feature resolution more closely
matches real world features. As map scale decreases,
resolution also diminishes because feature boundaries must
be smoothed, simplified, or not shown at all. 2. The size of
the smallest feature that can be represented in a smface. 3.
The number of points in x and y in a grid (e.g., the
resolution of a USGS one-degree DEM is 1.201 x 1.201
mesh points).2
Rubber-sheet - A procedure to adjust the entities of a
geographic data set in a non-uniform manner. From- and to-
coordinates are used to de£me the adjustment.
SARA - State Archives and Records Administration
Seale- the relationship between a distance on a map and
the corresponding distance on the earth. Often used in the
form I :24,000, which means that one unit of measurement
on the map equals 24,000 of the same units on the earth's
surface.
Scanner - A scanner is aa optical device that recognizes
dark and light dots on a surface and converts this
recognition into a digital fde. However, scanners generally
do not create a map database in a logically correct format,
so additional computer-aided manipulation and often
manual editing are used to add intelligence required by a
specific GIS platform.
Scanning - Also referred to as automated digitizing or
scan digitizing. A process by which information originally
in hard copy format (paper print, mylar transparencies,
micro£flm aper0~re cards) can be rapidly converted to digital
raster form (pixels) using optical readers.
Schematic Map - A map prepared by electronically
scanning or digitizing in which the lines are not
dimensionally or positionally accurate.
SDTS - Spatial Data Transfer Standard
SED - State Education Department
SEMO - State Emergency Management Office
Server - software that allows a computer to offer a service
to another computer. Other computers contact the server
program by means of matching client software. Also a
computer using server software.
Source Material - data of any type required for the
production of mapping, charting, and geodesy products
including, but not limited to, ground-control aerial and
terrestrial photographs, sketches, maps, and charts;
topographic, hydrographic, hypsographic, magnetic,
geodetic, oceanographic, and meteorological irfformatinn;
intelligence documents; and written reports pertaining to
natural and human-made features.
Spatial Data - data pertaining to the location of
geographical entities together with their spatial
dimensions. Spatial data are classified as point, line, area,
or surface.
Spatial Index - A means of accelerating the drawing,
spatial selection, and entity identification by generating
geographic-based indexes. Usually based on an internal
sequential numbering system
Spatial Model - Analytical procedures applied with a
GIS. There are three categories of spatial modeling
functions that can be applied to geographic data objects
within a GIS: (1) geometric models (such as calculation of
Euclidian distance between objects, buffer generation area,
and perimeter calculation); (2) coincidence models (such as
a polygon overlay); and (3) adjacency models (patlrfmding,
redistricting, and allocation). All three model categories
support operations on geographic data objects such as
points, lines, polygons, TINs, and grids. ]:unctions are
organized in a sequence of steps to derive the desired
information for analysis.
Stakeholders - Any constituency in the environment
that is affected by an organization's decisions and policies.
26 GIS Development Guide
Standards - In computing, a set of rules or specifications
which, taken together, define the architecture of a hardware
device, program, or operating system.
State Plane Coordinate System The plane-
rectangular coordinate systems established by the United
States Coast and Geodetic Survey (now known as National
Ocean Survey), one for each state in the United States, for
use in defining positions of geodetic stations in terms of
plane-rectangnlar (X and Y) coordinates. Each state is
covered by one or more zones, over each of winch is placed
a grid imposed upon a conformal map projection. The
relationship between the grid and the map projection is
established by mathematical analysis. Zones of limited
east-west dimension and indefinite north south extent have
the transverse Mercator map projection as the base for the
state coordinate system, whereas zones for winch the above
order of magnitude is reversed have the Lambert conformal
conic map projection with two standard parallels. For a
zone having a width of 158 statute miles, the greatest
departure from exact scale (scale error) is 1 part in 10,000.
Only adjusted positions on the North American datum of
1927 and NAD 1983 may be properly transformed into
plane coordinates on a state system. All such geodetic
positions which are determined by the National Ocean
Survey are transformed into state plane-rectangular
coordinates on the proper grid, and are distributed by that
bureau with the geodetic positions. State plane coordinates
are extensively used in recording land surveys, and in many
states such use has received approval by legislative
SUNY - State University of New York
System - A group of related or interdependent elements
that function as a unit.
Tax Map - An accurate map of a municipal territory
prepared for the purpose of taxation. Showing among other
things, the location and width of streets, roads, avenues
and each individual lot of land within the municipality.
Text Data - Information in a GIS system such as
property owners' names and lot dimensions.
Thematic Layer - mapping categories, consisting of a
single type of data such as population, water quality, or
timber stands, intended to be used with base data.
Thematic Map A map that illustrates one subject or
topic either quantitatively or qualitatively.
Theme . A collection of logically organized geographic
objects defined by the user. Examples include streets,
wells, soils, and streams.
TIGER - supersedes DIME (se* entry) f'das.
TIGER- See Topologically Integrated Geographic
Encoding and Referencing
Topographic Map - A map of land-source features
including drainage lines, roads, landmarks, and usually
relief, or elevation.
Topologically Integrated Geographic Encoding
and Referencing data (TIGER) - A format used by
the US Census Bureau to support census programs and
surveys. It is being used for the 1990 census. TIGER files
contain street address ranges along lines and census
tract/block boundaries. These descriptive data can be used
to associate address information and census/demographic
data to coverage features.
Topology The spatial relationships between
connecting or adjacent coverage features (e.g., arcs, nodes,
polygons, and points). For example, the topology of an
arc includes its from- and to- nodes and its left and right
polygons. Topological relationships are built from simple
elements into complex elements: points (simplest
elements), arcs (sets of connected points), areas (sets of
oounected arcs), and mutes (sets of sections) that are arcs or
portions of arcs). Redundant data (coordinates) are
eliminated because an arc may represent a linear feature,
part of the boundary of an area feature, or both. Topology
is useful in GIS because many spatial modeling ope'rations
don't require coordinates, only topological information.
For example, to find an optimal path between two points
requires a list of which arcs connect to each other and the
cost of traversing along each arc in each direction.
Coordinates are only necessary to draw the path after it is
calculated.
Transformation - The process of converting data from
one coordinate system to another through translation,
rotation, and scaling .
Transmission Control Protocol (TCP) - One of the
protocols on which the Internet is based.
Vectors - Lines defined by 'x", "y" and "z" coordinate
endpoints. Roads, rivers, contour lines, etc. presented as
vector lines.
Vector Data - A coordinate-based data structure
commonly used to represent map features. Each hnear
feature is represented as a list of ordered x, y coordinates.
Attributes are associated with the feature (as opposed to a
raster data structm'e, which associates attributes with a grid
ccH). Traditional vector data structures include double-
digitized polygons and arc-node models.
Vector Display: A vector display on a computer screen
is produced by drawing vectors on the screen. A raster
display, in contrast, is produced on a screen as rows of dots
of "on" or "off which produce the picture.
Wide Area Network (WAN) - a network that uses high-
speed, long distance communications networks or
satellites to connect computers over distances greater than
those traversed by local area networks (LANs)--about 2
miles.
Workstations and Terminals A workstation is a
device or a combination of devices integrated to provide
the user with graphic data en~-y, display, and manipulation.
These devices are used for map digitizing and map-related
applications, geographic analysis and ad hoc query. Most
systems still use some type of inexpensive edit-query
workstations or termnials to provide low-cost access to
beth maps and related date.
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Local Government
GIS Development Guides
Needs Assessment
. ,.,..~'.~ .~,- ~ ~t ·
Prepared by:
Erie County Water Authority
National Center for Geographic
Information and Analys~s, SUNY at Buffalo
GIS Resource Group, Inc.
Supported by:
New York State Archives and Records Administration
June, 1996
GIS DEVELOPMENT GUIDE: NEEDS ASSESSMENT
~ INTRODUCTION
A needs assessment is the first step in implementing a successful GIS within any
local government. A needs assessment is a systematic look at how departments function and the
spatial data needed to do their work. In addition to the final needs assessment report that is
generated, intangible benefits are realized by an organization. Conducting a GIS needs assessment
fosters cooperation and enhanced communication among departments by working together on a
common technology and new set of tools. Finally, the needs assessment activity itself serves as a
learning tool where potential users in each participating department learns about GIS and how it
can serve the department.
A needs assessment is required if the local government will be adopting a GIS throughout the
organization. Without a complete needs assessment each department might proceed to adopt their
own system and database which may or may not be compatible with those of another department.
The largest benefit for a local government adopting a GIS is to realize efficiencies from common
"base data" and the sharing of data among departments.
At the conclusion of a needs assessment, an organization will have all of the information needed to
plan the development of a GIS system. This information can be grouped into the following
categories:
Applications to be developed. - In evaluating the responsibilities and work flow within a
deparUnent~ certain tasks are identified that can be done more efficiently or effectively in a GIS.
These tasks will form the basis of GIS applications. Application descriptions prepared as part
of the needs assessment will describe these tasks.
GIS Functions required. - For each application identified, certain GIS functions will be
required. These will include standard operations such as query and display, spatial analysis
functions such as routing, overlay analysis, buffering, and possibly advanced analysis
requiring special programming.
Data needed in the GIS database. - Most departments in local government use data that
has a spatial component. Much of this data are hardcopy maps or tabular data sets that have a
spatial identifier such as addresses and zip codes or X-Y values (latitude-longitude, state plane
coordinates, or other coordinate system). A needs assessment will identify how this
information will be used by GIS applications.
Data maintenance procedures. - By looking at the work flow and processes within and
between departments, responsibility for data creation, updates and maintenance will become
apparent.
INote: The needs assessment procedme refers to a local government and its departments as the organizational units. I[
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In a multi-agency GIS cooperative, the same activities described would be carried out by all payticipants, at thell
appropriate level of detail as determined by the role each participant would play in the resulting GIS cooperative.
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28 GIS Development Guide
Once all of this information is collected and analyzed for each department and published in a report,
it can be used as a blueprint for implementing the GIS. The GIS coordinating group within the
organization will use it to:
· Design the GIS database
· Identify GIS software that will meet the government's needs
Prepare an implementation plan
· Start estimating the benefits and costs of a GIS
A common mistake in performing a needs assessment is to simply take an inventory of the maps
and spatial data currently used in each department. There are two major problems with this
approach. First, this does not allow the GIS coordinating group to evaluate how a GIS could be
used to enhance the work of each department and the agency as a whole. By looking at the
department functions and what the department does or produces, the GIS coordinating group and
potential users develop an understanding of the role GIS can play in the organization. The existing
data and maps do need to be inventoried and may well be used in building the GIS, however such
an inventory should be separate from the needs assessment.
The second major problem with the "data inventory" approach is that it tends to focus only on data
internal to the organization. Local governments rely heavily on data from outside sources - federal
agencies, state agencies, business, etc. The need for these data is better determined by looking at
the potential GIS applications and how data will be used by each application. It can then be
determined what data should be acquired from other sources.
~ CONDUCTING A NEEDS ASSESSMENT
The most significant aspect of a needs assessment is to document the findings in a standard and
structured manner. It is very important to adopt (or develop) a standard method to be used for the
description of all the GIS tasks, processes and data that will be included in the needs assessment.
These forms will be used in needs assessment to identify the three kinds of GIS requirements:
GIS applications - these will be tasks that can be performed by the GIS when a user
requires them, such as preparing a map, processing a query, or conducting some particular
GIS analysis. GIS applications can be described using the five page GIS Applications forms
included with this guide as Appendix A.
G1S activity - these are situations where information needs to be kept on some activity or
process important to the user, such as issuing building permits, conducting public health
inspections, etc. A GIS activity can be described using pages 1 and 4 of the GIS Applications
forms - the mare application form and the data flow diagraming (DFD) form.
GIS data - there will be certain categories of spatial data that are important to keep, but which
will not appear in any GIS application or activity identified in any application description. A
separate method must be developed to systematically record the need for such data. Other GIS
data needed but not included in either of the above categories, can be entered directly into the
master data list.
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Needs Assessment 29
The main method used to collect the information to enter onto the forms is individual interviews.
Potential users of the GIS can be identified by management and by examination of the organization
chart. A series of one-on-one interviews is the best way to identify the users needs. During the
interview, the user can usually identify documents that can provide additional information to the
GIS analyst.
· The needs assessment activity is composed of two main parts
· Interviewing and documenting the needs of potential GIS users
· Compiling the results of the needs assessment into the master data list and the list
of GIS functions. These two lists respectively are used to prepare the GIS data
model and the GIS specifications (activities described under Conceptual Design).
The interview process should identify and describe all anticipated uses of the GIS. The next
section briefly describes the major categories of GIS use, followed by a detailed description on
how to complete the needs assessment forms.
~ LOCAL GOVERNMENT USES OF GIS
The use of geographic information systems by local government falls into five major categories:
· Browse
· Simple display (automated mapping);
· Query and display;
· Map analysis; and
· Spatial modeling.
Browse
This function is equivalent to the human act of reading a map to find particular features or patterns.
Browsing usually leads to identification of items of interest and subsequent retrieval and
manipulation by manual means. For single maps, or relatively small areas, the human brain is very
efficient at browsing. However, as data volumes increase, automated methods are required to
effectively extract and use information from the map.
Simple Display
This GIS function is the generation of a map or diagram by computer. Such maps and diagrams are
often simple reproduction of the same maps used in a previous manual oriented GIS environment.
Examples of this type of use are preparation of a 1:1000-scale town map, a sketch of an approved
site plan, maps of census data, etc.
30 GIS Development Guide
Query And Display
This function supports the posing of specific questions to a geographic database, with the selection
criteria usually being geographic in nature. A typical simple query would be: "draw a map of the
location of all new residential units built during 1989" A more complex query might be: "draw a
map of all areas within the town where actual new residential units built in 1989 exceeds growth
predictions." Such a query could be part of a growth management activity within the town. Queries
may be in the form of regular, often asked questions or may be ad hoc, specific purpose questions.
The ability to respond to a variety of questions is one of the most useful features of a GIS in its
early stages of operation. In the long mn, other more sophisticated applications of the GIS may
have a higher value or benefit, but to achieve these types of benefits, users must be familiar with
the GIS and its capabilities. Such familiarization is achieved through the use of a GIS for the
simpler tasks of query and display.
Map Analysis (Map Overlay)
This involves using the analytical capabilities of GIS to de£me relationships between layers of
spatial data. Map analysis is the super-imposition of one map upon another to determine the
characteristics of a particular site (e.g., combining a land use map with a map of flood prone areas
to show potential residential areas at risk for flooding). Map analysis (often termed overlay or
topological overlay) was one of the first real uses of GIS. Many government organizations,
particularly those managing natural resources, have a need to combine data from different maps
(vegetation, land use, soils, geology, ground water, etc.). The overlay function was developed to
accomplish the super-imposition of maps in a computer. The data are represented as polygons, or
areas, in the GIS data base, with each type of data recorded on a separate "layer." The combination
of layers is done by calculating the logical intersection of polygons on two or more map layers. In
addition to combining multiple "layers" of polygon-type data, the map overlay function also
permits the combination of point data with area data (point-in-polygon). This capability would be
very useful in a town for combining street addresses (from the Assessor's files) with other data
such as parcel outlines, census tract, environmental areas, etc. Many facility siting problems,
location decisions, and land evaluation studies have successfully used this procedure in the past.
Spatial Modeling
This application is the use of spatial models or other numerical analysis methods to calculate a
value of interest. The calculation of flow in a sewer system is an example of spatial modeling.
Spatial modeling is the most demanding use of a GIS and provides the greatest benefit. Most
spatial modeling tasks are very difficult to perform by hand and are not usually done unless a
computerized system, such as a GIS, is available. These models allow engineers and planners to
evaluate alternate solutions to problems by asking "what if' type questions. A spatial model can
predict the result expected from a decision or set of decisions. The quality of the result is only as
good as the model, but the ability to test solutions before decisions have to be made usually
provides very useful information to decision makers. Once again, this type of use of a GIS will
evolve over time, as the GIS is implemented and used.
A closely related computer capability is a CAD system (computer aided design). CAD systems are
used to prepare detailed drawings and plans for engineering and planning applications. While CAD
systems functions are different from GIS functions, many commercial CAD products have some of
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Needs Assessment 31
the functionality normally found in a GIS. There are, however, significant differences between a
CAD system and a GIS, mainly in the structure of the data base. There may be some need for
CAD-type capabilities in a particular local government, so this forms another category of use.
In general, geographic information in local government is used to:
· Respond to public inquiries,
· Perform routine operations such as application reviews and permit approvals, and
· Provide information on the larger policy issues requiting action by the town board.
These are typical local government activities which benefit from a geographic information system.
The development of GIS will facilitate the present geographic information handling tasks and
should lead to the development of additional applications of benefit to the local government.
There are also other computer systems in local governments that perform GIS-like functions, such
as Emergency 911, underground utility locator systems, school bus routing systems, etc. The
variety and diversity of GIS applications are what make the definition of a GIS very difficult.
Basically, any computer system where the data have one or more spatial identifiers or that perform
spatial operations can be classed as a GIS. For example, a system containing street addresses and
census tract codes and that has the ability to place a given street address in the proper census tract is
a GIS whether or not map boundaries are pan of the system. There are two important points here:
A large proportion of local government data does have one of more spatial identifiers,
and therefore has the potential of being pan of a GIS.
Other, existing systems with GIS data or performing GIS-like functions must be
integrated into the overal system design. GIS should not be developed as a separate
system.
Whether a local government unit is considering or planning a "full, multi-purpose GIS" or is only
interested in a limited or single function system, the database planning and design considerations
are the same. Only the magnitude of the analysis and design activities differ. Some GIS users
believe that smaller and simpler applications, such as a school bus routing system, do not require a
formal planning activity. There are, however, several reasons to conduct such a planning activity
for the smaller applications:
· To ensure that the user requirements will be fully met
· To develop documentation, especially data documentation (metadata), needed to use
and maintain the GIS
· To be in a position to participate in data sharing programs with other agencies as
additional applications are developed
· To create a permanent record of the data and its use to document agency plans and
decisions, and to meet data retention and archiving requirements.
· To use as a base for building a larger, multi-function at some later date.
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32 GIS Development Guide
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The level of effort needed to complete a GIS plan can be kept commensurate with the scope and
size of the intended GIS. Further, the GIS planning software tool that accompanies these
guidelines provides an easy and convenient way to create the recommended documentation.
~DATA USED BY LOCAL GOVERNMENT
There are many kinds of data used by local government that can be included in a GIS. Data in a
GIS can be one of two types: spatial data and non-spatial data. Spatial data is that data which is
taken from maps, aerial photographs, satellite imagery, etc. It is composed of spatial entities,
relationships between these entities, and attributes describing these entities. Non-spatial data is
usually tabular data taken from tables, lists, etc. Most of the time, the non-spatial data will be
linked to one or more spatial entities by keys (unique identifiers associated with the spatial data and
non-spatial data). For example, the tax map would represent the spatial data while the real property
inventory is non-spatial data, which is linked to the entities(parcels) on the tax map.
Spatial data is commonly represented by geometric objects (points, line, and polygons). Non-
spatial data containing a spatial reference is also considered spatial data. One of the most common
forms of this type of data in local government are records and fries referenced by street address.
Examples of local government data that have been used with GIS include:
Tax parcels
Real property inventories
Infrastructure data
Water system
Sewer system
Electric
Census data
Land use maps
Zoning maps
Planimetrics
Right-of-way
Waterways (streams)
Building Outlines
Permit records
The operations required in a GIS must meet the data handling requirements of the spatial data as
well as those of the non-spatial data. The most common use of a GIS in local government is the
query based on attribute keys and then displayed in map form.
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Needs Assessment 33
~ DOCUMENTING GIS NEEDS
The GIS needs are documented using the following forms (full-page sized copies of all forms are
included in Appendix A):
The GIS Application Description (5 pages) used to:
· Describe products (mostly map displays) produced by the GIS
· Describe activities supported by the GIS
The Master Data List
Most GIS applications can be described using the GIS Application Description. In cases where
these forms are not appropriate, any other systematic description of the need can be used. If more
appropriate, different forms can be developed as long as the same information can be
systematically recorded: the data required and the GIS functions need to develop the GIS product.
G1S Application Description
The set of forms used to document a GIS contains five pages:
Figure 1 - GIS Application Descriptions
GIS Application Description (Page A- 1)
Use to enter:
- Application identification
- Description of purpose
- Type of application, map scale, query key,
frequency, and required response time
- Data needed by the application
- Entities (features)
- Attributes of entites
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Map Display (Page A- 2)
Used to draw a sample of any maps to be
produced by the application (including the
legend showing symbols for each feature).
This can be a hand sketch, although it should
be drawn to the scale of the output desired.
Table Display (Page A- 3)
Used to show samples of any tables to be
produced by the application (used only if
tables are needed in the application). If any
entries in the table involve complex
calculations, these should be described using
either a Data Flow Diagram (page 4) or other
separate pages.
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Needs Assessment 35
Data Flow Diagram (Page A-4)
Used to draw a data flow diagram or flow
chart when an application is complex. This
chart is usually drawn by the GIS analyst or
someone else familiar with the diagraming
techniques, and is used to document
complex calculations or descriptions of
activities that will need GIS support.
Entity-Relationship Diagram (Page A- 5)
Used to draw an entity-relationship (E-R)
diagram of the data used in the application.
This drawing is usually done by the GIS
analyst or someone else familiar with the
E-R technique, and is only done for mom
complex GIS applications.
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36 GIS Development Guide
~ DOCUMENTING AN ACTIVITY-TYPE USE OF THE GIS
Some GIS applications in local government do not involve the production of maps and tables. For
example, a GIS may be used to record and store information about a building permit application, a
subdivision plat, a site plan, etc. Many activities of local government are simply the processing of
permits from individuals or firms. If any of these activities will also generate GIS data, they should
be described for the needs assessment. Two techniques available for describing processes are flow
charts and data flow diagrams.
A completed application description for a local government activity of this type can be entered on
pages 1 and 4 of the GIS Application Description forms. Page 4 - Data Flow Diagram would
appear as follows:
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Resident
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ITown
Resident
SBL # Index
Figure 2 - Data Flow Diagram Example
This example shows a data flow diagram that has three participants (town resident, planning
department, and assessor's department) that uses three parts of the database (zoning map, section-
block-lot number index, and tax map), to answer a zoning inquiry. Appendix D contains a brief
description of the data flow diagraming method.
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Needs Assessment 37
~?THE MASTER DATA LIST
The master data list is a composite of all data entities (features) and their attributes that have been
entered in the data section of the GIS Application Description (Page 1). Other data identified by
users as "needed," but not included in any application description may be entered directly into the
master data list.
Master Data List
Entity Attributes Spatial
Object
Street_segment
Street intersection
Parcel-
Building
Occupancy
Street_segment
Street_intersection
Water_main
Valve
Hydram
Service
Soil
Wetland
Floodplain
Traffic_zone
Census_tract
Water_District
5oning
name, address_range Line
street_names Line
section_block_lot#, Polygon
owner_name, owner_address, site_address,
area, depth, front_footage, assessed_value,
last sale date, last_sale_price, size
owner_name, owner_address, assessed_value
(as of previous January lst)
building_ID, dam_built, Footprint
building_material, building_assessed_value
occupant_name, occupant_address, None
occupancy_type_code
name, type, width, Polygon
length, pavement_type
length, width Polygon,
traffic flow conditions, intersecting_streets
type, size, material, installation_date Line
type, installation_dam Node
type, installation_date, Node
pressure, last_pressure test date
name, address, type, invalid_indicator None
soil_code, area Polygon
wetland_code, area Polygon
flood_code, area Polygon
zone_IDg, area Polygon
Iract#, population Polygon
name, ID_number Polygon
zonins_code, area Polygon
Figure 3 - Master Data List
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38 GIS Development Guide I
~ CONDUCTING INTERVIEWS
Individual interviews are the most effective way of f'mding out from users their potential GIS
applications. Before starting interviews, a briefing session for all potential users should be held.
During this meeting, the interviewers should describe the entire needs assessment procedure to all
participants. The main activities will be:
· Conduct "start-up" seminar or workshop
· Interview each potential user
· Prepare documentation (forms) for each application, etc
· Review each application description with the user
· Obtain user approval of and sign-off for each application description
An introductory seminar or workshop with all potential users in attendance is useful to prepare the
way for user interviews. At the beginning of a project, many users may not have much knowledge
about GIS or how it might help them. Also, the interview team may be from outside the
organization and may not be very familiar with the structure of the particular local government.
The start-up seminar should address the following topics:
Definitions:
What is a GIS?
How is a GIS used by local government? (Typical applications)
Interview procedure to be followed: What the interviewee will do?
What is expected from the interviewee?
Who approves the application descriptions?
How the information from the application descriptions will be used?
Group discussion: It is often useful to have the group identify an initial set of GIS
applications as candidates for further documentation. The discussion of possible
applications between interviewers and users will start to reveal what is suitable for a
GIS application. One or more applications can be described in the process by the group
so everyone sees how the process will work.
It is preferable to interview users individually rather than in groups. This provides a better
opportunity to explore the ideas of each person and also prevents other individuals from
dominating any particular meeting. Group meetings easily lose focus on specific GIS applications
and therefore do not provide the detailed information needed to adequately describe the GIS
applications.
Conducting an interview is not an easy task. Some potential users may have a good grasp of GIS
and how they might use one. However, often potential users do not have complete knowledge of
the capabilities of a GIS and therefore may not be able to readily identify GIS applications. In these
cases, the interviewer (GIS analyst) needs to help the user explore his/her job activities and
responsibilities to identify GIS oppommities. The GIS analyst should usually begin an interview
with a review of the procedure, then ask the user to identify and describe potential applications.
When specific GIS applications cannot be easily identified, it is helpful if potential users describe,
in general, his/her job functions and responsibilities and the role their department plays in the
whole organization. From this discussion, the GIS analyst can usually identify potential GIS
applications and then explore these for possible inclusion in the needs assessment.
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I Needs Assessment 39
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Need to make a map Need to save Need to descdbe
I Need to answer a query impo~ant data an activity
Add lo Master Data List
I Prepare l ~plication Prepare Data
Descd )tion t Flow Dia~gram
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Figure 4 - Interviewing and Documenting Needs of a Potential GIS User
40 GIS Development Guide
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~ PREPARING THE NEEDS ASSESSMENT REPORT
The needs assessment report consists of the application descriptions, the master data list, and
several summary tables. A list of all applications summarizing the type and frequency of use is the
first table.
~pp # Application Name Type Frequency
Zoning Query Query & Display 85 / day
2 Customer Phone Inquiry Query & Display 100/day
Fire Dispatch Map Query & Display 86/day
Fire Redistricting Map Map Analysis i/year
Crime Summary Map Query & Display 12/month
Patrol Dispatch Map Query & Display 133/day
Complaint Summary Map Query & Display 624/year
Subdivision Development Map Query & Display No estimate
Counter Query Map Query & Display 85/day
Land Use/Land Value Map Display 1/year
Assessed Value Map Query & Display 144/year
Grievance Map Query & Display 2500/year
Comparable Value Map Query & Display No estimate
Built/Vacant Map Display 1/year
Water and Sewer Line Map Query & Display 30/month
Hydrologic Proffie Map Spatial Model 1440/year
Sewer System Flow Analysis Spatial Model 12/year
Emergency Repair Map Query & Display 110/year
Storm Drainage Map Spatial Model 700/year
Fire Flow Test Map Spatial Model 260/year
Easement Map Query & Display 520/year
Zoning Map Query & Display 50/day
Floodplain Map Query & Display 50/day
Youth League Residency Check Query & Display 3500/year
Mosquito Control Area Map Query & Display 50/year
Site Plan Approval Process Query & Display 200/year
Census Data Map Display 48/year
Population Density Map Map Analysis 50/year
Land Use Inventory Display 24/year
Retail Space Projection Spatial Model 24/year
Office Space Projection Spatial Model 12/year
Traffic Volume Map Query & Display 24/year
List of GIS Applications
'3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
3O
31
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Figure 5
~This table contains selected GIS applications from the Town of Amhe. rst~ N.Y. Needs Assessment
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Needs Assessment 41
Figure 6 - Table Summarizing Applications Example
The data from the first table can be used to prepare tables summarizing applications by department
and the frequency of applications by department.
INumbers in these tables are from the Town of Amherst, N.Y. needs assessment and represent the estimates of GIS R
use per year. These numbers will be used during the database Planning and Design phase to estimate usage andll
benefits, of the GIS. In this example, for the Town of Amherst, it is estimated that 2.5 minutes of staff time will be II
saved for each query giving a total savings of 4.03 years staff time/year (202,281 times 2.5 minutes divided by 60Il
m~nutes/hour divided by 2088 hours per year), q
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The last table relates GIS applications to the data used by each application.
This matrix is very useful in planning and
scheduling data conversion. If applications
are prioritized, then data needed by high
priority applications can be scheduled for
conversion early in the conversion process.
Also, if some data is not available for some
reason, it is possible to determine the
affected applications.
Figure 7 - GIS Applications/Data Matrix
The last step in compiling the needs assessment report is to extract the list of GIS functions needed
from the application descriptions. This list will include the standard function types of display and
query and display plus any other functions included in a data flow diagram or flow chart. Typical
examples of such GIS functions are: calculate distance between objects, determine the shortest path
through a network, etc. Figure 8 is an example of a GIS functions list.
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42 GIS Development Guide
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GIS Functions Needed:
Candidate GISs
GIS Functions Generic GIS ARC/INFO INTERGRAPH SYSTEM 9
(from Applic. Desc Functions Basic Macro Basic Macro Basic Macro
31SPLAY SCREEN DISPLAY ARCPLOT YES YES
PLOTTER DISPLAY ARCPLOT YES YES
3ENERATE REPORT INFO YES YES
;~U ERY ~,TTRIBUTE QUERY INFO YES YES
~PATIAL QUERY SPATIAL SEARCH IDENTIFY YES YES
MAP ANALYSIS OVERLAY ARC YES YES
BU~-~-bH ARC YES YES
RECLASSIFY ARC YES YES
~HOHI I-S I PAIH SH(JHIbST I~AI H N~- FW(JHK NO YES
ROUTE ROUTE NETWORK NO YES
HYDRAULIC AML YES YES
MODEL
Figure 8 - GIS Function List
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Needs Assessment 43
Application L~St Ot Data Flow
Description Important Diagram
Data
Master
Data I_ist
List of GIS
Functions
Figure 9 - Compiling Results of Needs Assessment Example
The list of GIS functions and the master data list will be used in subsequent tasks to design the
database and prepare the GIS specifications.
44 GIS Development Guide
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SUMMARY
The procedure presented in the guideline for preparing a needs assessment is based on
documenting GIS applications in a standard format. The components of this format are structured
to facilitate communication between potential GIS users and the GIS analyst, and to provide
specific and detailed information to the GIS analyst for designing the GIS. The first page of the
application description is the most critical to the GIS analyst as it contains the list of data and an
indication of the GIS functionality required by the application. If additional information on the
GIS functionality is needed, than a flow chart or data flow diagram can be developed (page 4 of the
application description). For the potential user, the map display and report format describe output
he/she will receive. These pages should be sufficiently detailed for the user to approve or sign-off
as to the correctness of the application description. It is, of course, very important that the entire
GIS application description be internally consistent.
The entity-relationship diagram (page 5) is mainly useful in the next phase of the GIS design -
Conceptual Design, where the data model for the entire system will be defined. If entity-
relationship diagrams are prepared for individual applications, they will than be available for the
Conceptual Design phase. Otherwise, these diagram can be prepared during the Conceptual Design
phase.
Figure 9 is a diagrammetric representation of the flow of information from the elements of the
application description to the master data list and the list of GIS functions.
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Appendix Table of Contents
Appendix A - GIS Application Description Forms
GIS Application Description ............................................................. A- 1
Map Display ................................................................................... A-2
Table Display .................................................................................. A-3
Data Flow Diagram ......................................................................... A-4
Entity-Relationship Diagram ............................................................. A-5
Appendix B
Master Data List .............................................................................. B-1
Appendix C - Sample GIS Application Descriptions
Customer Phone Inquiry, Erie County Water Authority ...................... C-1
Erie County Map Guide, Erie County Public Works Dept .................... C-4
Job Training Site Selection, Erie County Social Services Dept .............. C-5
Appendix D
Data Flow Diagraming ..................................................................... D- 1
Appendix E
List of Application Name, Type, & Frequency ................................... E-1
,A~pplication Descriptions .................................................................. E-2
~waster Data List .......................................................... E-17
Summary Table of Depts. & Counts of Application Type .................... E-21
Summary Table of Depts. & Annual Frequencies of Application Type.E-22
Name of Government
Geographic Information System
Requirements Analysis
Application identification #:
Application Name:
Department:
Defined by:
Purpose and Description:
Type of Application:
Display Display/Map ScaJe:
Query Query Key:
Query & Display Response Time:
Map Anatysis Frequency:
Spatial Model
Data Required:
Features (entities): Attributes:
Prepared by: Approved by: Date:
Name of Government
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Depar~nent:
Defined by:
Graphical Output Sample:
Screen:
Hard Copy:
Symbols~Legend
Prepared by: Approved by:
Date:
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Name of Government
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
Report Layout/Format:
Screen: Hard Copy:
HEADINGS
SUB-HEADINGS
SUB-TOTALS/TOTALS:
Prepared by: Approved by: Date:
.4,-3
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Name of Government
Geographic Information System I
Requirements Analysis I
Application Identification #: I
Application Name:
Department:
Defined by:
Process Description: Data Flow Diagram or Flow Chart I
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Prepa y: App y: Date: I
Name of Government
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
Data Description: Entity - Relationship Diagram
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N
Prepared by: Approved by:
Date:
.4,-5
Entity Attributes Spatial
Object
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Street_segment
Street_intersection
Parcel
Building
Occupancy
Street_segment
Street_intersection
Water_main
Valve
Hydrant
Service
Soil
Wetland
Floodplain
Traffic_zone
Census_tract
Polygon
Water_district
Zoning
name, address_range Line
street,_names Line
section_block_lot#, Polygon
owner_name, owner_address,
site_address, area, depth,
front_footage, assessed_value,
last sale date, last_sale_price,
size (owner_name,
owner_address,
assessed_value as of previous
January 1st)
building_ID, date_built, Footprint
building_material,
building_assessed_value
occupant_name, None
occupant_address,
occupancy_type_code
name, type, width, length, Polygon
pavement_type
length, width, traffic flow conditions Polygon
intersecting_streets
type, size, material, installation_date Line
type, installation_date Node
type, installation_date, pressure Node
last~Dressure test date
name, address, type, invalid_indicator None
Soil_code, area Polygon
wetland_code, area Polygon
flood_code, area Polygon
zone_ID#, area Polygon
tract#, population
name, ID_number
zoning_code, area
Polygon
Polygon
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Erie County Water Authority
Geographic Information System
Requirements Analysis
Application Identification #: 19
Application Name: Customer Phone Inquiry
Department: Dispatch
Defined by: T. May
Purpose and Description:
To respond to phone inquires of: 1) 'no water;' or 2) to take requests for
service. (Reference Donohue #18)
Type of Application:
Display Display/Map Scale: 1' = 100'
Query Query Key: Address
Query& Display XX Response Time: 10 seconds
Map Analysis Frequency: xxJday
Spatial Model
Data Required:
Features (entities): Attributes:
ROW
Pipe
Parcel
Building
Services
Projects
Work_orders
Location (boundary), street name,
street_address_range
Location (line), size
Location (boundary), address
Location (footprint)
Location(parcel), address, name, status
Location (boundary), current_in_progress
Location (parcel_by_address), current,
date work_order_number
Prepared by: Approved by:
Date:
Erie County Water Authority
Geographic Information System
Requirements Analysis
Application Identification #: 19
Applicatk)n Name: Customer Phone inquiry
Deparlment: Dispatch
Defined by: T. May
Graphical Ou~ut Sample: Screen: XX Hard Copy:
I 30 I 31 I I 2 I 3 I 4 I 5[ 6 I 7 I
~ ~ 18
Symbols/Legend
...... Parcel Water Main
-- ROW -- -- ,-- Service Connection
Prepared by: Approved by: Date:
~...~j Building
Erie County Water Authority
Geographic Information System
Requirements Analysis
Application Identification #: 19
Application Name: Customer Phone Inquiry
Department: Dispatch
Defined by: T. May
Report Layout/Formah Screen: XX Hard Copy:
Oustomer Service Inquiry
qame Address Status Pipe Size Project Work Order
,I.J. Jones 1551 51st Ave. Active 4 in. None None
Prepared by: Approved by: Date:
C-3
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County of Erie
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
1
Erie County Map Guide
Public Works
Roger Fik
Purpose and Description:
To provide a general multi-purpose map of Erie County for public use.
Type of Application:
Display X Display/Map Scale: 1'=2 miles
Query Query Key: N/A
Query & Display Response '13me: 5 to 10 minutes
Map Analysis Frequency: Yearly publication
SpatiaJ Model
Data Required:
Features {entities): Attributes:
County Boundary Location, Name (line)
Townships L(~cation, Name (Polygon)
Cities Location, Name (Polygon)
Villages Location, Name (Polygon)
Communities Location, Identitier (Node)
County Roads Location, Name (Line)
City, Town, & Village Roads Lccation, Name (Line)
State Highways Location, Name (Line)
Interstate, State Thruway, & Expressways L~cation, Name (Line)
Interstate Route Numbers Route Iden§tier, Loca~on
State Route Numbers Route Identifier, Location
US Route Numbers Route Idenf~fier, Location
Reservations Location, Name (Polygon)
State Parks Location, Name (Polygon)
County Parks Location, Name (Polygon)
County Forssts Location, Name (Polygon)
Sf~earns, Rivers, & Creeks Location, Name (Line)
Water Bodies Location, Name (Polygon
Airports L~cation, Name (Node)
County Jurisdiction Designation Location, Name (Node)
Prepared by J. Volpe: Approved by:
Date: 3/15/94
(;-4
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County of Erie
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Deper~nent:
Defined by:
Purpose and Description:
48
Job Training Site Location
Sociar Services
Jeff Embury (C/O Jim Kubacki)
To provide trainees with an adequate training site while
minimizing the distance they must travel to reach that site.
Type of Application:
Display Display/Map Scale: Multiple
Query Query Key: Trainee Address
Query & Display X Response Time: < 1 Minute
Map Analysis Frequency: Daily
Spatial Model
Data Required:
Features (entities): Attributes:
ROADS XY_Location, Name, Address_Range
TRAINEE Trainee_Address, Trainee_Name
TRAINING SITE Site_Name, Site_Address, Site_Phone #
SUBWAY XY_Location, Subway_Stop_Name.
Subway_Stop_Locafion
BUS ROUTES XY_Location, Busreute_Number,
Bus_Stop_Name, Bus_Stop_Location
Prepared by: Approved by: Date:
(;-5
Geographic Information System
Requirements Analysis
AA pP pplii~c~ t~ nn ~daer~' 'eft:cafl°n #: j4o8b Training Site Location
,
Prepared by: Edc Covino Approved by: Date: 5/5/94
C-6
Name of Government
Geographic Information System
Requirements Analysis
Application Identification #: 48
Application Name: Job Training Site Location
Deparb'nent: Social Services
Defined by: Jeff Embury (C/O JimKubacld)
Process Description: Data Flow Diagram or Flow Chart
rn;
Overlay
Training
Sites
.~ File of Trainee Placement
Prepared by: Approved by: Date:
Name of Government
Geographic Information System
Requirements Analysis
Application Identification #: 48
Applica~on Name: Job Training Site Location
Department: Social Services
Defined by: Jeff Embury (C/O Jim Kubacld)
Process Description: Data Flow Diagram or Flow Chart
BUS ROUTE
ROAD
Address TRAINEE
Ma~h
JOB SITET
Mak:fl
SUBWAY
Prepared by: Approved by: Date:
C-$
Data Flow Diagraming
Data flow diagrams offer a standardized method of portraying processes, data stores, and
participants that make up a logical activity potential GIS application). Four symbols are used
in a data flow diagram:
A square represents people,
organizations, things,
or sources or destinations of
data or information
A cylindrical shape to represent
a process or activity
An open rectangle to represent
a data stored from
which data can be added or
removed
An arrow to represent data
flows. Arrow can be
annotated as necessary to
describe nature or content flow.
D-1
Appl#
11
12
13
14
15
16
17
19
28
29
36
37
41
63
70
List of Application Name, Type, and Frequency
Application Name Type Frequency
Subdivision Development Map Query & Display 1 per month
Counter Query Map Query 50 per day
Land Use/Land Value Map Display 1 per year
Assessed Value Map Query & Display 3 per year
Grievance Map Query & Display 1650 per year
Comparable Property Map Query & Display 1 per month
Built/Vacant Map Display 1 per year
Sanitary Sewer Line Map Query & Display 2 per week
Public Improvement Map Query & Display 10 per week
Total Committed Flow Map Spatial Model 20 per week
Storm Sewer Map Display 10 per day
Youth League and Residency Check Map Query 1500 per year
Optimal Snow Removal Route Map Spatial Model 10 per month
Population Density Map Browse 50 per year
Population Projection Spatial Model 4 per year
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Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
11
Subdivision Development Map
Assessor
H. Williams
Purpose and Description:
To monitor the progress of development of an approved subdivision (how many lot$ are built
the rote of the building).
I Type of Application:
Query & Display
Display/Map Scale: 100;200;400
Response Time:
Frequency: 1 per month
Data Required:
Feature Spatial Object
Attribute
Pamel Polygon
location
Street (double line) Polygon
name
location
Subdivision Polygon
name
location
Approved by:
E-2
Prepared by:
Date: 03-June-96
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
12
Counter Query Map
Assessor
H. Williams
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Purpose and Description:
To provide a quick query of one or more parcels and the associated parcel data (mostly ARLM file
data) for answering inquiries at the counter or over the telephone.
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Type of Application:
Query
Data Required:
Feature
Building
Parcel
Street (center line)
Prepared by:
DisplayfMap Scale: 50;100;200;400
Response Time:
Frequency: 1 per month
Spatial Object
Attribute
Polygon
assessed value
building #
Polygon
subdivision lot
SBL#
location
Line
length
address range
name
location
Approved by:
E-3
Date: 03-June-96
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
13
Land Use/Land Value Map
Assessor
H. Williams
Purpose and Description:
To produce a display of the value of land per square foot and/or front footage by land use type.
I Type of Application:
Display
Data Required:
Feature
Parcel
Street (center line)
Prepared by:
Approved by:
E-4
Display/Map Scale: 200;400
Response Time: 1 week
Frequency: 1 per year
Spatial Object
Attribute
Polygon
front footage
size
last sale price
land use code
location
Line
location
Date: 03-Jtme-96
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
14
Assessed Value Map
Assessor
H. Williams
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Purpose and Description:
To produce a map showing the assessed values (by range) for a small area; or for designated
neighborhoods.
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Type of Application: DisplayfMap Scale: 400
Query & Display Response Time: Interactive
Frequency: 3 per year
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Data Required:
Feature
Neighborhood
Parcel
Street (double line)
Prepared by:
Approved by:
E-5
Spatial Object
Attribute
Polygon
location
Polygon
assessed value
location
Polygon
name
location
Date: 03-June-96
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
15
Grievance Map
Assessor
H. Witliams
Purpose and Description:
To show assessed values of properties in the same area as a parcel where a grievance is ~ed.
Type of Application:
Query & Display
Display/Map Scale: 100;200;400
Response Time: interactive
Frequency: 1650 per year
Data Required:
Feature
Parcel
Street (double line)
Prepared by:
Approved by:
E-6
Spatial Object
Attribute
Polygon
assessed value
location
Polygon
name
location
Date: 03-June-96
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
16
Comparable Property Map
Assessor
H. Williams
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Purpose and Description:
Show the comparable properties selected to determine the assessed value of a given property.
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Type of Application:
Que~ & Display
I
Data Required:
Feature
Parcel
Street (double line)
Prepared by:
Display/Map Scale: 100;200;400
Response Time:
Frequency: 1 per month
Spatial Object
Attribute
Polygon
address
assessed value
location
Polygon
name
location
Approved by:
E-7
Date: 03-June-96
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Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
17
Built/Vacant Map
Assessor
H. Williams
Purpose and Description:
To display the built and vacant parcels
I Type of Application:
Display
Display/Map Scale: 400
Response Time: Interactive
Frequency: 1 per year
Data Required:
Feature
Occupancy
Parcel
Street (double line)
Spatial Object
Attribute
Node
occupant type code
occupant address
Occupant name
Polygon
built/vacant code
location
Polygon
nfli1]e
location
Prepared by:
Approved by:
Date: 03-June-96
E-8
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
19
Sanihary Sewer Line Map
Assessor
H. Williams
Purpose and Description:
To show the location of sanitary sewer lines for the purpose of approving digging activities.
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Type of Application:
Query & Display
Display/Map Scale: 50;1000
Response Time: 5 min.
Frequency: 2 per week
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Data Required:
Feature
Building footprint
Manhole
Sanitary sewer line
Sidewalk
Storm sewer line
Street (double line)
Wye hook ups (new only)
Prepared by:
Approved by:
E-9
Spatial Object
Attribute
Polygon
business name
building name
Node
depth
location
Line
location
Line
location
Line
location
Polygon
name
location
addr~s range
Nrxle
distance from manholes
location
Date: 03-June-96
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Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
28
Public Improvement Map
Engineering
P. Bowers
Purpose and Description:
To show facilities near a certain p0.rcel for review of a public improvement permit or site plan.
Type of Application:
Quet~ & Display
Display/Map Scale: 100;200
Response Time: 30 sec
Frequency: 10 per week
Data Required:
Feature Spatial Object
Attribute
Parcel Polygon
location
Sanitary sewer Line
location
Storm drainage Line
location
Sweet (double line) Polygon
cu.tb location
pavement type
location
Water main Line
installation date
material
size
type
location
Prepared by:
Approved by:
E-10
Date: 03-June-96
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
29
Total Committed Flow Map
Engineer
P. Bowers
· Purpose and Description:
To keep track of the total committed flow of sanitary and storm sewers.
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Type of Application: Display/Map Scale: 1000
Spatial Model Response Time: 1 min
Frequency: 20 per week
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Data Required:
Feature Spatial Object
Attribute
Detention pond Polygon
capacity
size
location
Ditches Polygon
capacity
size
location
Monitoring point Node
location
Sanitary sewer line Line
capacity
size
location
Storm sewer line Line
capacity
size
locainn
Street (center line) Line
location
Prepared by: Approved by:
E-11
Date: 03-June-96
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Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
36
Storm Sewer Map
Building Department
T. Ketchttra
Purpose and Description:
To display the location of storm sewers.
I Type of Application:
Display
Display/Map Scale:
Response Time:
Frequency:
100;200
12 sec
10 per day
Data Required:
Feature
Contoul's
Easement
Manhole
Parcel
Storm sewer line
Street (double line)
Prepared by:
Approved by:
E-12
Spatial Object
Attribute
Line
location
elevation
Polygon
location
type
Node
location
invert elevation
rim/surface elevation
Polygon
location
Line
location
Polygon
name
location
Date: 03-June-96
Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
37
Youth League and Residency Check Map
Recreation Department
J. Bloom
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Purpose and Description:
To determine the appropriate league for a resident (by parcel) and discover non-resident
applications.
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Type of Application: Display/Map Scale: 1000
lQuery Response Time: 30 sec
Frequency: 1500 per year
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Data Required:
Feature
League
Parcel
Prepared by:
Approved by:
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Spatial Object
Attribute
Polygon
type
location
Polygon
owner a~kkcss
land use
location
Date: 03-June-96
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Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
41
Optimal Snow Removal Route Map
Highway DeparUnent
F. Jurgens
Purpose and Description:
To calculate the most efficient routes for snow removal and salting.
Type of Application:
Spatial Model
Display/Map Scale: 1000
Response Time: 1 week
Frequency: 10 per month
Data Required:
Feature
Street (center line)
Street intersections
Traffic zone
Spatial Object
Attribute
Line
length
class
wklth
location
Node
traffic flow conditions
Polygon
zone code
Prepared by:
Approved by:
Date: 03-June-96
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Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
63
Population Density Map
Planning
G. Black
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Purpose and Description:
To browse population density by census tract, block group, or block.
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Browse
Display/Map Scale: variable: 200 to 1000
Response Time: Interactive
Frequency: 1 per year
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Data Required:
Feature
Census Block
Census tract
Parcel
Street (center line)
Prepared by:
Approved by:
E-15
Spatial Object
Attribute
Polygon
block #
population total
location
Polygon
U-act #
location
Polygon
area
land use code
location
Line
name
location
Date: 03-June-96
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Geographic Information System
Requirements Analysis
Application Identification #:
Application Name:
Department:
Defined by:
70
Population Projection
Planning
C. Brown
Purpose and Description:
To estimate future population of the Town, by small area (census tract, block group, and possibly
block).
Type of Application:
Spatial Model
Display/Map Scale: 1000
Response Time: 1 day
Frequency: 4 per yea~
Data Required:
Feature Spatial Object
Attribute
Census Block Polygon
block #
size
location
Census tract Polygon
tract #
size
location
Net migration None
application #69
Wetland Polygon
area
wetland code
Zoning Polygon
zoning code
Prepared by:
Approved by:
E-16
Date: 03-June-96
Feature
Building
Building footprint
Census Block
Census tract
Contours
Detention pond
Ditches
Easement
League
Manhole
Monitoring point
Master Data List
Attribute
assessed value
building #
address
building name
business name
block #
location
p.opultion total
size
location
size
tract #
elevation
location
capacity
location
size
capacity
location
size
location
location
depth
invert elevation
location
rim/surface elevation
location
E-17
Spatial Object
Polygon
Polygon
Polygon
Polygon
Line
Polygon
Polygon
Polygon
Polygon
Node
Node
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Master Data List Cont'd
Neighborhood
Net migration
Occupancy
Parcel
Sanitary sewer line
Sidewalk
Storm drainage
Storm sewer line
location
name
application # 69
occupant address
occupant name
occupant type code
address
area
assessed value
builffvacant code
depth
front footage
land use
land use code
last sale price
location
owner address
owner name
SBL #
size
subdivision lot
capacity
location
size
capacity
location
size
E-18
Polygon
None
Node
Polygon
Lille
Line
Lme
Line
I
Master Data List Confd
Street (center line)
Street (double line)
Street intersections
Subdivision
Traffic zone
Water main
Weti~d
Wye hook ups (new only)
Zoning
class
length
location
name
width
address range
address range
curb location
location
name
pavement type
street names
traffic flow conditions
boundary
name
area
zone code
installation date
location
material
size
area
wetland code
distance from manholes
location
zoning code
E 19
Line
Polygon
Node
Polygon
Polygon
Line
Polygon
node
Polygon
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GIS Application by Department by Type
Department Browse Display Query QueD' Spatial Total
& Display Model
Assessor 0 2 1 4 0 7
Building Dept. 0 I 0 0 0 1
Engineering 0 0 0 2 1 3
Highway Dept. 0 0 0 0 1 1
Planning 1 0 0 0 1 2
Recreation Dept. 0 0 1 0 0 1
Total 1 3 2 6 3 15
GIS Application by Department by Frequency
DeparUnent Browse Display Query Query Spatial Total
& Display Model
Assessor 0 2 18250 1677 0 19929
Building Dept~ 0 3650 0 0 0 3650
Engineering 0 0 0 624 1040 1664
Highway Dept. 0 0 0 0 120 120
Planning 50 0 0 0 4 54
Recreation Dept. 0 0 1500 0 0 1500
Total 50 3652 19750 2301 1164 26917
E-20
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Local Government
GIS Development Guides
Prepared by:
Erie County Water Authority
National Center for Geographic
Information and Analysis, SUNY at Buffalo
GIS Resource Group, Inc.
Supported by:
New York State Archives and Records Administration
June, 1996
GIS DEVELOPMENT GUIDE: CONCEPTUAL DESIGN OF THE GIS
PART 1 - DATA MODELING
INTRODUCTION
This guide describes data modeling in general, spatial data modeling in specific, the setting of
GIS specifications, and an introduction to spatial data and metadata standards. These activities
are collectively called conceptual design of the GIS system (Figure 1). This activity takes
the information developed during the Needs Assessment and places it a structured format. The
result of this activity will be a GIS data model and functional specifications for the
GIS system.
Benchmark
Fi ure 1 - GIS Development Process
Conceptual design is the first step in database design where the contents of the intended
database are identified and described. Database design is usually divided into three major activities
Conceptual data modeling: identify data content and describe data at an abstract, or
conceptual, level. This step is intended to describe what the G1S must do and does
not deal with how the GIS will be implemented - the "how" question is the
subject of logical and physical database design;
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46 GIS Development Guide
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Logical database design: translation of the conceptual database model into the data
model of a specific software system; and
Physical database design: representation of the logical data model in the schema of the
software.
Data Objects
Identified Dudng
Needs Assessment
Initial
Metadata
to Metadata
Match Needed Data I <~
to Available Data
and Sources
Prepare Detailed
Database Plan
GIS Database
Confinalng GIS
Database Maintenance
Archives
Figure 2 - Life Cycle of a GIS Database
Source Documents:
Maps, Images, Air
Photos, etc.
Survey and Evaluation
of Available Data
Map and Tabular
Data Convemion
Database QJVQC EdfiJng
Database Backups
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Conceptual Design of the GIS 47
The conceptual design of the GIS system is primarily an exemise in database design. Database
planning is the single most important activity in GIS development. It begins with the
identification of the needed data and goes on to cover several other activities collectively termed the
data life cycle - identification of data in the needs assessment, inclusion of the data in the data
model, creation of the metadata, collection and entry into the database, updating and maintenance,
and, finally, retained according to the appropriate record retention schedule (Figure 2). A
complete data plan facilitates all phases of data collection, maintenance and retention and as
everything is considered in advance, data issues do not become major problems that must be
addressed after the fact with considerable difficulty and aggravation.
The conceptual design of the GIS also includes identification of the basic GIS architecture
(functions of hardware and GIS software), estimates of usage (derived from the needs
assessment), and scoping the size of the GIS system. All of this is done with reference to the
existing data processing environments (legacy systems) that must interface with the GIS.
Preparing A GIS Data Model
A data model is a formal definition of the data required in a GIS. The data model can take one of
several forms, the two used in this guideline are a structured list and an entity-relationship
diagram. The purpose of the data model, and the process of specifying the model, is to ensure
that the data has been identified and described in a completely rigorous and unambiguous
fashion and that both the user and GIS analyst agree on the data definitions. The
data model is then the formal specification for the entities, their attributes and all
relationships between the entities for the GIS.
Building a data model is not necessarily an easy task. Most professionals in local government will
not have had experience in this task. The GIS analyst of the project is the individual who either
should build the data model or acquire assistance, such as a qualified consultant, to complete this
task. If the opportunity exists for the GIS analyst to attend a database design course or seminar,
this would enhance this person's ability to build the model but, more importantly, provide the
knowledge for using the final data model in building the GIS. To the extent that data models
prepared for other local governments match the needs of a particular GIS development program, or
can be easily adapted, they can be modified for use as the data model. However, the GIS analyst
must have a good understanding of the resulting model and how it is used to build and manage the
GIS database.
The next sections of the guideline first discuss the nature of geographic data, then present
the methodology used for data modeling, and lastly describe the development of a GIS data
model from the information collected during the Needs Assessment. The example provided in the
last section is actually a sample local government GIS data model and is suitable for direct use,
with appropriate modification to specific situations.
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48 GIS Development Guide
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NATURE OF GEOGRAPHIC DATA
Geographic data describe entities which have a location. The geographic data includes the
location information and other information about the entity of interest. This other information will
be referred to as attributes of the entities. Historically several terms have been used to describe
the data in a GIS database, among them features, objects, or entities. The term feature
derives from cartography and is commonly used to identify "features shown on a map," while
entity and object are terms from computer science used to identify the elements in a database.
The normal dictionary definitions of these terms are:
Object: a thing that can be seen or touched; material thing that occupies space
Entity: a thing that has definite, individual existence in reality
Feature: the make, shape, form or appearance of a person or thing
A good GIS database design methodology requires the use of terms in a clear an
unambiguous manner. This guideline will use the term entity to represent objects or things to be
included in the database and attribute will be the term for representing the characteristics or
measurements to be recorded for the entities. Other terms have commonly been used to describe
the organization of entities and attributes in a GIS, such as layer, coverage, base map,
theme, and others. Each of these will usually refer to a collection of one or more entities
organized in some useful way which is specific to the GIS software in use. These terms will
become important during the logical/physical database design activities where decisions about
how the GIS data are to be stored in the GIS database are made. The conceptual database design
activity is focused solely on specifying what is to be included in the GIS database and should
provide clear and unambiguous representation of the entire GIS database.
In addition to a clear and concise definition of entities and their attributes, data modeling describes
relationships between entities. An example of a relationship between an employee and a
company would be "works for."
Employee - Works For - Company
Relationships may be bi-directional, thus:
Company - Has - Employees
An important aspect of a relationship is "cardinality," that is if the relationship is between only one
of each entity or ff either entity may be more than one. For example, one company usually has
many employees whereas one employee works for only one company. The possible cardinalities
are: one-to-one; one-to-many; and many-to-many. Thus:
--- Has --->
Company (One) <--- Work For ...... (Many) Employees
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Conceptual Design of the GIS 49
There are many variations of the notation used to express these facts. The notation recommended
for local govemment will be described later.
Geographic, or spatial data, differs from other "regular" data that are included in
computer databases in how entities are defined and in the relationships between entities. Entity
identification for spatial data includes the definition of a physical or abstract entity (e.g., a
building) and the definition of a corresponding spatial entity (i.e., a polygon to
represent the building footprint). This latter, or second entity does not exist for other types
of computer databases. The existence of the corresponding spatial entity is one of the major
factors that distinguishes GIS from other types of systems and is what makes it very important to
utilize proper planning and design techniques when building a GIS. An example will be used to
illustrate this difference.
Entities:
Physical or -.....
Conceptual
'"'"Entity and I Spatial Entity
Its Attributes * and Attributes
Pamel (owner_name, owner_address)
Street_segment (name, type, width)
Building (date_built, assessed_value)
Soil-type (soil_code, area)
Landuse_area (land_use, code, area)
Polygon (coordinates, topology)
Line_segment (coordinates, topology)
Footprint (coordinates)
Polygon (coordinates, topology)
Grid_cell (coordinates)
Figure 3 - Examples of Physical or Conceptual Entities and Their Corresponding
Spatial Entities
ENTITY-RELATIONSHIP (E-R) DATA MODELING
To start the discussion of entity-relationship modeling, two examples will be shown. One, a
regular database and the second, a simple GIS database. The personnel database in any local
government could have entities of employee, dependent and department.
Relationships between these entities would be employee" works in" department and dependent "is
a member of" the employee's family. Some of the attributes for each entity would be as follows:
Employee (name, age, sex, job title)
Dependent (name, age, relationship_to _employee, i.e., spouse, child, etc.)
DeparUnent (deparUnent_name, function, size)
50 GIS Development Guide I
A diagrametric representation of the example would be as follows: I
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Polygon
Parcel
Figure 4 - Example of a Firm's Database
An example of a simple spatial database would be a follows:
Parcel ID#, owner_name, owner_address, site_address
Building Building_name, height, floor_area
Occupant Occupant_name, un/t_number
The diagrammatic form of this spatial database would be as follows:
Building I
Occupant
Figure 5 - Example of a Simple GIS Database
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This example has been presented using two standard notational forms for conceptual
database design: a relation, the entity name followed by a list of attributes; and an entity-
relationship diagram showing entities, their attributes, and the relationships between entities.
On figure 5, there are two things to notice:
· The standard entity - relationship diagram has no provision for representing the
corresponding spatial entity (point, line, polygon) of the data; and
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Conceptual Design of the GIS 51
· The representation of the attributes (ellipses) can be somewhat awkward due to
different name lengths and the number of attributes to be shown.
The two notational forms modified to accommodate GIS data will be used as the primary tools for
conceptual database design in this guideline; however, modifications will be made to adequately
represent GIS data. The next section will provide the formal definition of the basic entity-
relationship data modeling method, the modifications needed to represent GIS data, followed by
examples of GIS data entities and attributes typical for local government and the by a description
of how to model these data using the modified entity-relationship data modeling technique.
Basic Entity-Relationship Modeling
The basic entity-relationship modeling approach is based on describing data in terms of the three
parts noted above (Chert 1976):
· Entities
· Relationships between entitles
· Attributes of entities or relationships
Each component has a graphic symbol and there exists a set of rules for building a graph (i.e., an
E-R model) of a database using the three basic symbols. Entities are represented as rectangles,
relationships as diamonds and attributes as ellipses.
The normal relationships included in a E-R model are basically those of: 1. Belonging to;
2. Set and subset relationships;
3. Parent-childrelationships; and
4. Component parts of an object.
The implementation rules for identifying entities, relationships, and attributes include an
English language sentence structure analogy where the nouns in a descriptive sentences identify
entities, verbs identify relationships, and adjectives identify attributes. These rules have been
defined by Chen (1983) as follows:
Rule 1: A common noun (such as person, chair), in English corresponds to an entity type
on an E-R diagram.
Rule 2: A u-ansitive verb in English corresponds to a relationship type in an E-R diagram.
Rule 3: An adjective in English corresponds to an attribute of an entity in an E-R diagram.
English statement: Mr. Joe Jones resides in the Park Avenue Apartments which is located on land
parcel g01-857-34 owned by die Apex Company.
Analysis: .. "Joe Jones"," "Park Avenue Apartments," "land parcel" and "Apex Company" are
nouns and therefore can be represented as entities "occupant," "building," "parcel," and "owner."
"resides," "located on" and "owned by" are transitive verbs (or verb phrases) and therefore def'me
relationships.
52 GIS Development Guide I
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Example of Simple E-R diagrams
Name: Joe Jones
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Figure 6 Shows a Simple E-R Diagrams of the Previous Example
Many times it is possible to build different E-R diagrams for the same data. For example, instead
of creating the entity "owner" in the above example, the owner's name could be an attribute of
parcel (shaded areas of figure 6). During the process of building an E-R diagram (i.e., the
conceptual model) for a database, the analyst must make decisions as to whether something is best
represented as an entity or as an attribute of some other entity.
The process of constructing an E-R diagram uncovers many inconsistencies or contradictions in the
definition of entities, relationships, and attributes. Many of these are resolved as the initial E-R
diagram is constructed while others are resolved by performing a series of transformations on the
diagram after its initial construction. The final E-R diagram should be totally free from de£mitional
inconsistencies and contradictions. If properly constructed, an E-R diagram can be directly
converted to the logical and physical database schema of the relational, hierarchical or network type
database for implementation.
Unique Aspects of Geographic Data
In the simplest terms, we think of geographic data as existing on maps as points, lines and areas.
Early GIS systems were designed to digitally encode these spatial objects and associate one or
more feature codes with each spatial feature. Examples would be a map of land use polygons, a
set of points showing well locations, a map of a stream shown as line segments. For the purposes
of plotting (redrawing the map) a simple data structure linking (x,y) coordinates to a feature code
was sufficient.
Topology
A distinguishing feature of a modem GIS is that some spatial relationships between spatial entities
will be coded in the database. This coding is termed topologically coding. Topology is
based on graph theory, where a diagram can be expressed as a set of nodes and links in a
manner that shows logical relationships. Applied to a map, this concept is used to abstract the
features shown on the map and to represent these features as nodes and arcs (point and lines).
Nodes are the end-points of arcs and areas are formed by a set of arcs. If the concept and
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Conceptual Design of the GIS 53
definitions of topologic data structures are not familiar to the reader, the following readings are
recommended:
· Geographic Information Systems: A Guide to the Technology, by John
Antenucci, et. al, pages 98-99.
· Fundamentals of Spatial Information Systems, by Robert Lauring and Derek
Thompson, pages 206-211.
· ARC/INFO Data Model, Concepts, & Key Terms, by Environmental Systems
Research Institute, Inc., pages 1-12 to 1-15.
Coordinate strings without topology with associated feature codes were called "spaghetti" fries
because there was not any relationship between any two coordinate strings formally encoded in the
database. For example, the "GIS system" would not "know" if two lines intersect or not or
whether they had common end points. These relationships could be seen by the human eye if a
plot were to be made or alternatively could be calculated (often a time consuming process). Typical
of this type of geographic data file are those produced by computer-aided drafting systems (CAD),
or known as .dxf, .dwg, or .dgn files.
GEOGRAPHIC DATA MODELS
The data models in most contemporary GISs are still based on the cartographic view. Other data
models have begin to evolve, but are still very limited. Current and potential geographic data
models include:
The cartographic data model: points, lines and polygons (topologically encoded) with
one, or only a few, attached attributes, such as a land use layer represented as polygons
with associated land used code
· Extended attribute geographic data mode: geometric objects as above but with many
attributes, such as census tract data sets;
Conceptual object/spatial data model: explicit recognition of user defined objects, zero
or more associated spatial objects, and sets of attributes for reach defined object
(example: user objects of land parcel, building, and occupant, each having its own set
of attributes but with different associated spatial objects: polygon for land parcel,
footprint for building, and no spatial object of occupant).
Conceptual objects/complex spatial objects: multiple objects and multiple associated
spatial objects (example: a street network with street segments having spatial
representations of both line and polygon type and street intersections having spatial
representations of both point and polygon type).
Current GIS are based on the caxtographic and extended attribute data models. The trend to object-
oriented computer systems and databases will require that GIS planners view their databases from
an "object viewpoint."
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Spatial Relationships
GISs also differ from other systems in that they include spatial relationships. These relationships
are included in the GIS either by the topologic coding or by means of calculations based on the
(x,y) coordinates. One common calculation is whether or not two lines intersect. Table 1 shows
the spatial relationships, associated descriptive verbs, and the common implementation of each
relationship by a GIS.
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Spatial Relationships
Spatial Descriptive Common GIS E-R Model
Relationship Verbs Implementation Symbol
Connect, link Topology
Connectivity
Adjacent'
Contiguity abutt Topology
Contained, X, Y coord.
Containment containing, operation
within
Proximity Closest, X,Y coord.
nearest operation
Coincidence Coincident, X,Y coord.
Coterminous operation
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Figure 7 - Spatial Relationships in a GIS
Connectivity and contiguity are implemented through topology: the link-node structure for
connectivity through networks and the arc-polygon structure for contiguity. Containment and
proximity are implemented through x,y coordinates and related spatial operations: containment is
determined using the point-, line-, and polygon-on-polygon overlay spatial operation and
proximity is determined by calculating the coordinate distance between two or more x,y coordinate
locations. The spatial relationship of coincidence may be complete coincidence or partial
coincidence. The polygon-on-polygon overlay operation in ARC/INFO TM calculates partial
coincident of polygons in two different coverages. The System 9 TM Geographic Information
System recognizes coincident features through a "shared primitive" concept (the geometry of a
point or line is stored only once and then referenced by all features sharing that piece of geomelxy).
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Conceptual Design of the GIS 55
Future versions of commercial GISs will likely implement coincident features through either the
"belonging to" database relationship or through x,y coordinates and related spatial operations,
whichever is more efficient within the particular GIS.
In summary, them are three types of relationships that will be represented in a geographic database
with an "object view" orientation:
· Normal database relationships, which are represented in a relational database by means
of keys (primary and secondary)
· Spatial relationships represented in the GIS portion of the database by topology
· Spatial relationships that exist only after a calculation is made on the (x,y) coordinates
METHODOLOGY FOR MODELING
Modeling a geographic database using the E-R approach requires an expanded or extended concept
for:
· Entity identification and definition; and
· Relationship types and alternate representational forms for spatial relationships.
There are three considerations in the identification and definition of entities in a geographic
database:
Correct identification and definition of entities
Entities in a geographic database are defined as either discrete objects (e.g., a building, a bridge, a
household, a business, etc.) or as an abstract object defined in terms of the space it occupies (e.g.,
a land parcel, a timber stand, a wetland, a soil type, a contour, etc.). In each of these cases we are
dealing with entities in the sense of "things" which will have attributes and which will have spatial
relationships between themselves. These "things" can be thought of as "regular" entities.
Defining a corresponding spatial entity for each "regular" entity
A corresponding spatial entity will be one of the spatial data types normally handled in a GIS, e.g.,
a point, line, area, volumetric unit, etc. The important distinction here is that we have a single
entity, its spatial representation and a set of attributes; we do not have two separate objects
(Figure 3 illustrates this concept). A limited and simple set of spatial entitles may be used, or
alternatively, depending on the anticipatetl complexity of the implemented geographic information
system, an expanded set of spatial entities may be appropriate. The corresponding spatial entity for
the regular entity may be implied in the definition of the regular entity, such as abstract entities like
a wetland where the spatial entity would normally be a polygon, or a contour where the spatial
entity would be a line. Other regular entitles may have a less obvious corresponding spatial entity.
Depending on the GIS requirements, the cartographic display needs, the implicit map scale of the
database and other factors, an entity may be reasonably represented by one of several
corresponding spatial entities. For example, a city in a small-scale database could have a point as
its corresponding spatial entity, while the same city would have a polygon as its corresponding
spatial entity in a large-scale geographic database.
56 GIS Development Guide
Recognize multiple instances of geographic entities, both multiple spatial
instances and multiple temporal instances
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Multipurpose (or corporate) geographic databases may need to accommodate multiple
corresponding spatial entities for some of the regular entities included in the GIS. For example,
the representation of an urban street system may require that each street segment (the length of
street between two intersecting streets) be held in the GIS as both a single-line street network to
support address geocoding, network based transportation modeling, etc., and as a double-line (or
polygon) street segment for cartographic display, or to be able to locate other entities within the
street segment (such as a water line), etc. In each of these instances the "regular" entity is the street
segment, although each instance may have a different set of attributes and different corresponding
spatial entities. Also, there may be a need to explicitly recognize multiple temporal instances of
regular entities. The simple case of multiple temporal instances Mil be where the corresponding
spatial entity remains the same, however, future GISs will, in all likelihood, have to deal with
multiple temporal instai~ces where the corresponding spatial entity changes over time.
Three symbols are defined to represent entities: entity (simple); entity (multiple spatial
representations); and entity (multiple time periods). The internal structure of the entity symbol
contains the name of the entity and additional information indicating the corresponding spatial
entity (point, line or polygon), a code indicating topology, and a code indicating encoding of the
spatial entity by coordinates (Figure 8). The coordinate code is, at the present time, redundant in
that all contemporary GISs represent spatial entities with x,y coordinates. However, it is possible
that future geographic databases may include spatial entities where coordinates are not needed.
Similarly, topological encoding is normally of only one type and can, for the present, be indicated
by a simple code. However, different spatial topologies have been defined and may require
different implementations ih a GIS (Armstrong and Densham, 1990). In the furore, the topology
code may be expanded to represent a specific topologic structure particular to a GIS application.
Object ~-- Regular Object Name
(entity)
Object G [ T ~
Topology
Indicator
~ 2 XY Coordinate Indicator
Ass
Spatial Object
Spatial Obiect
Type
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Figure 8 - Entity Symbol for Spatial Objects
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Conceptual Design of the GIS 57
Modeling Spatial Relationships
The spatial relationships are defined by three relationship symbols (Figure 9). The traditional
diamond symbol can be used for normal database relationships. An elongated hexagon and a double
elongated hexagon, are defined to represent spatial relationships. The elongated hexagon represents
spatial relationships defined through topology (connectivity and contiguity) and the double
elongated hexagon represents spatial relationships defined through x,y coordinates and related spatial
operations (coincidence, containment and proximity). The appropriate "verbs" to include in the
hexagonal symbols are the descriptors of the spatial relationships (as shown in Figure 7). The spatial
operation will be implicitly defined by the relationship symbol (double hexagon), the spatial entity
and the topology code. For example, a spatial relationship named "coincident" between entities
named "wetlands" and "soils," both of which cant topologic codes and x,y coordinates, indicates the
spatial operation of topological overlay. If this does not sufficiently define the spatial operation
needed, the name of the spatial operation can be used to describe the relationship, such as shortest
path, point-in-polygon, radial search, etc.
Figure 9 shows
all symbols needed to construct an Entity-Relationship dial~ram for
Basic E-R Symbolocly
I Entity
E-R Symbology for
Snatio-Temooral Data
Entity: simp~ with
eo~eesponding
spatial entity
Entity: m uRiple
temporal
GIS database.
Figure 9 - Extended Entity - Relationship Symbology for Designing
GIS Databases, Source: Calkins, 1996
58 GIS Development Guide I
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~ DEVELOPING A SPATIAL DATA MODEL
(ENTITY-RELATIONSHIP DIAGRAM) I
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· The GIS application descriptions
· The master data list: Lists, entities, corresponding spatial entities and attributes I
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~o~o~ I~ I· !
The information needed to develop the E-R diagram representing the spatial data model comes from
the Needs Assessment activity as:
· The list of functional capabilities (spatial operations)
The process of building the E-R diagram involves taking entities from the master data list one at a
time and placing each one on the diagram. For each new entity, any relationship to any previously
entered entity should be entered. Relationships are found by examining the Application
Descriptions and determining if the GIS processes require a specified operation. For example, if
an Application Description indicated that land parcels needed to be compared to a flood plain area,
then a spatial relationship of "coincident area" (or topological overlay operation) should be defined
between the two entities.
Land Parcel ~/"/Coincident
Po,ygon GIT ~ Area
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Figure 10 - Diagranmling a Spatial Relationship
As each entity is added to the E-R diagram, the list of attributes should be reviewed and checked to
determine if the attribute is appropriate for the entity, does not duplicate any other attribute or
entity, and can be rigorously defined for entry to create the metadata (metadata is discussed in the
next section of this guideline).
Figure 11 is a sample E-R diagram for data commonly used by local government. This example
contains 16 entities and 15 relationships. Attributes have not been included in the diagram in order
to reduce the size of the diagram for inclusion in this document.
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Conceptual Design of the GIS 5 9
Figure 11 - Entity Relationship Diagram for Selected Local Government Data
SUMMARY OF CONCEPTUAL DATA MODELING
The E-R diagram shown in Figure __ will be used to verify with the expected users the data
content of the GIS and, by additional reference to the GIS needs analysis, the required spatial
operations. Once verified by the users, the E-R representation can be mapped into a detailed
database design (as will be described in the Database Planning and Design Guideline)where:
1) Each entity and its attributes map into:
(a) One or more relational tables with appropriate primary and secondary keys (this
assumes the desired level of normalization has been obtained);
(b) The corresponding spatial entity for the "regular" entity. As most commercial GISs
rely on fixed structures for the representation of geometric coordinates and topology, this
step is simply reduced to ensuring that each corresponding spatial entity can be handled by
the selected GIS package;
2) Each relationship into:
(a) Regular relationships (diamond) executed by the relational database system's normal
query structure. Again, appropriate keys and normalization are required for this mapping.
(b) Spatial relationships implemented through spatial operations in the GIS. The
functionality of each spatial relationship needs to be described, and if not a standard
operation of the selected GIS, specifications for the indicated operation need to be written.
60 GIS Development Guide
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PART 2: SPATIAL DATA STANDARDS AND
METADATA REQUIREMENTS
Introduction
Spatial data standards cover a variety of topics including the definition of spatial data entities
(including a formal data model), methods of representation of the spatial entities in a GIS,
specifications for the transfer of spatial data between different organizations, and the definition of
the attributes of the spatial entities and the values these attributes may assume. Metadata is
"information about data," and should describe the characteristics of the data such as identifying
entities and attributes by their standard names and provide information on such items as data
accuracy, data sources and lineage, and data archiving provisions.
Much of the work on spatial data standards to date as been done under the auspices of the Federal
Geographic Data Committee and only concerns federal spatial data directly. The relationship
between the existing federal data standards and state and local spatial data standards have yet to be
developed. Appendix A contains a list of current and pending reports on federal spatial data
standards. Work towards New York State spatial data standards will be conducted under the
proposed GIS Standing Committee of the Information Resources Management Task Force.
Metadata for Local Governments in New York State
Metadata can serve many purposes. Some of the more important functions of metadata are:
Provide a basic description of a dataset
· Provide information for data transfers to facilitate data sharing
· Provide information for entries into clearinghouses to catalogue the availability of data
The metadata structure and content for local government recommended in this guideline has been
prepared according to the following criteria:
· The metadata must fa:st, and primarily, serve as a documentation and data management
tool for the data administrator in an agency or department
Secondly, the metadata must encompass and support the data manager and records
management officer in a local agency in all aspects of data management including data
definition, source documentation, management and updating, and data archiving and
retention requirement.
Thirdly, the metadata information must be able to generate and supply database
descriptions for spatial data clearinghouses such as the prototype New York State
Spatial Data Clearinghouse developed under the GIS Demonstration Project conducted
by the Center for Technology in Government, SUNY - Albany and any relevant federal
spatial data clearinghouses.
Conceptual Design of the GIS 61
The following metadata information is a prototype for a New York State Local Govemmem Spatial
Metadata Standard. This metadata is represented in a set of tables listed below and has been
implemented in Microsoft AccessTM. A working copy of this metadata program is available to all
local governments in the state. The structure and information on how to use the software are
described in a user's guide available with the program. The content of the metadata tables is as
shown in the following lists.
Metadata Tables
1. Organization Information
Name Of Organization
Depamnent
Room/Suite #
Number And Street Names
City
State
Zip Code
Phone Number
Fax Number
Contact Person
Phone Number/Extension
Email Address
Organization Intemet Address
Comments
2. Reference Information
Filename
File Format
Availability
Cost
File Intemet Address
Metadata Created By
Date Metadata Created
Metadata Updated By
Date Metadata Updated
Metadata Standard Name
Comments
3. Object/File Name Information
Filename
Data Object Name
4. Data Object Information
Distribution Filename (Same as Filename in Reference Information)
Dam Object Name
Type
Data Object Description
Spatial Object Type
Comments
62 GIS Development Guide
5. Attribute Information
Data Object Name
Data Attribute Name
Attribute Description
Amibute Filename
Codeset Name/Description
Measurement Units
Accuracy Description
Comments
6. Data Dictionary Information
Data Object Name
Data Attribute Name
Data Type
Field Length
Required
Comments
7. Spatial Object Information
Data Object Name
Spatial Object Type
Place Name
Projection Name/Description
HCS Name
HCS Datum
HCS X-Offset
HCS Y-Offset
HCS Xmin
HCS Xmax
HCS Ymin
HCS Ymax
HCS Units
HCS Accuracy Description
VCS Name
VCS Datum
VCS Zmin
VCS Zmax
VCS Units
VCS Accuracy Description
Comments
8. Source document information
Data Object Name
Spatial Object Type
Source Document Name
Type
Scale
Date Document Created
Date Digitized/Scanned
Digifi~ng/Scanning Method Description
Accuracy Description
Comments
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Conceptual Design of the GIS 63
9. Lineage Information
Data Object Name
Data Object 1
Data Object 2
Description of Spatial Operation and P~rameters
Accuracy Description
Comments
10. Update Information
Data Object Name
Update Frequency
Date
Updated By
Comments
11. Archive Information
Data Object Name
Retention Class
Retention Period
Data Archived
Archived By
Date to be Destroyed
12. Source Documents
Source Document Name
Source Document IDg
Source Organization
Type of Document
Number of Sheets (map, photo)
Source Material (paper, mylar)
Projection Name
Coordinate System
Date Created
Last Updated
Conu'ol/Accuracy (map, photo)
Scale
Reviewed by
Review date
Spatial extent
File format
Comments
13. Entities Contained in Source
Source 1I~
Entity Name
Spatial Entity
Estimated Volume of Spatial Entity
Symbol
Accuracy Description of Spatial Entity
Reviewed by
Review Date
Scrub Needed (yes/no)
Comments
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14. Attributes by Entity
Source
Entity Name
Attribute Description
Code Set Name
Accuracy Description of Attribute
Reviewed By
Review Date
Comments
Additional Reading
(the following material is quite technical, but a good set of sources on conceptual database design.)
Armstrong, M.P. and P.J. Densham, 1990, Database organization strategies for spatial decision
support systems, International Journal of Geographical Information Systems, vol. 4, no. 1, 3-20.
Calkins, Hugh W., Entity Relationship Modeling of Spatial Data for Geographic Information
Systems, Intemational Journal of Geographical Information Systems, January 1996.
Chen, P.P., 1976, The entity-relationship model - toward a unified view of data, ACM
Transactions on Database Systems, vol. 1, no. 1, March 1976, pp. 9-36
Chen, P.P., 1984, English sentence structure and entity-relationship diagrams, Information
Sciences, 29, 127-149
Davis, C., et. al., eds., 1983, Entity-Relationship Approach to Software Engineering, Amsterdam,
Netherlands: Elsevier Science Publishers B.V.
Elmasri, R. and S.B. Navathe, 1989, Fundamentals of Database Systems, Redwood City,
California: The Benjamin/Cummings Publishing Company, Inc.
Jajodia, S. and P. Ng, 1983, On representation of relational structures by entity-relationship
diagrams, Entity-Relationship Approach to Software Engineering, P. Ng and R. Yeh (eds.),
Amsterdam, Netherlands: Elsevier Science Publishers B.V., pp. 249-263.
Liskov, B. and S. Zilles, 1977, An introduction to formal specifications of data abstractions,
Current Trends in Programming Methodology - Vol. 1: Software Specification and Design, R.T.
Yeh (ed), Prentice Hall, pp 1-32.
Loucopoulos, P. and R. Zicari, 1992, Conceptual Modeling, Databases, and CASE: An integrated
view of information systems development, New York: John Wiley & Sons, Inc.
Teorey, T.J. and J.P. Fry, 1982, Design of Database Structures, Englewood Cliffs, NJ: Prentice-
Hall, Inc.
Ullman, J.D., 1988, Principles of Database and Knowledge-base Systems, 2 vols. (Rockville,
Maryland: Computer Science Press, Inc.)
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Appendix A
Developing Standards for Spatial Data and Metadata
Spatial data standards are needed in order to facilitate the exchange of spatial data between
geographic information systems. We refer to data as "spatial" because the common factor is a
geographic reference (a reference in space) which allows the data to be accessed through a GIS. In
order to accomplish the goal of facilitating data exchange, spatial data standards should provide:
· Definitions of terms for spatial objects or features included in GIS;
· A structure (or forma0 for the exchange of spatial data;
· A method for describing the accuracy and lineage of the data; and
· The definition of metadata (the data that describes the spatial data).
The primary purpose for spatial data standards is to facilitate data sharing and exchange, thus the
focus only on data issues. The Council concluded that It is not necessary to develop standards for
GIS hardware or software at this time. as these standards are expected to evolve from groups such
as the Open GIS Consortium, a non-profit trade association formed to implement the Open
Geodata Interoperability Specification.
The Current Status of Standards
At present, spatial data standards exist only at the Federal government level. Under the Federal
Geographic Data Committee, three standards documents have been prepared:
The Spatial Data Transfer Standard (SDTS - FIPS 173)
This standard defines a method for the exchange of spatial data between different GIS software
systems. It also contains definitions of terms for the spatial objects of interest to Federal
government agencies.
Content Standards for Digital Geospatial Metadata (proposed)
This standard defines the content for digital geospatial metadata, the information about spatial data
flaat would be entered into a clearinghouse or repository to form a catalog of spatial data available to
other users.
Cadastral Standards for the National Spatial Data Infrastructure (draft)
This is a draft standard for cadastral (land ownership) data, one of twelve theme standards
documents under preparation.
The Federal Geographic Data Committee has also established a National Spatial Data Infrastructure
(NSDI) for the purpose of coordinating geographic data acquisition and access. The mechanism for
this will be a National Spatial Data Clearinghouse, a distributed network of geospatial data
producers, managers, and users linked electronically. It is envisioned that this network of
clearinghouses would contain information about available spatial dam. Potential users would search
this clearinghouse to f-md data of interest, access the metadata for a description of data of interest,
and could acquire the data from the distributing agency. Spatial data may be deposited directly with
a clearinghouse or retained by the originator.
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The Federal effort towards standards development started in 1981 and The National Spatial Data
Infrastructure and Federal spatial data standards are still evolving at this time. The remaining
subject area (theme) standards reports are scheduled for release during the Spring of 1996 ( themes
are: base cartographic, bathymetric, cultural and demographic, geodetic, geologic, ground
transportation, international boundaries, soils, vegetation, water, and wetlands). The table below
shows the current status of federal spatial data standards development.
Implementation of the Federal geospatial data standards is through Executive Order 12906 signed
by the President on April 11, 1994. The FGDC is directed to" ...seek to involve State, local, and
tribal governments in the development and implementation of the initiatives continued in this
order." The Order provides that:
"Federal agencies collecting or producing geospatial data, either directly or indirectly -e.g. through
grants, partnerships, or contracts with other entities) shall ensure, prior to obligating funds for
such activities, that data will be collected in a manner that meets all relevant standards adopted
through the FGDC process. "
Status of Federal Geographic Data Committee Standards
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Currently in development:
National Spatial Data Accuracy Standard
Standards for Digital Orthoimagery
Draft Standards for Digital Elevation Data
Hydrographic and Bathymelric Accuracy Standard
Standards for Geodetic Conla'ol Networks
Transportation Network Profile for
Spatial Data Transfer Standard
Transportation-related Spatial Feature Dictionary
Soils Data Transfer Standard
Vegetation Classification Standards
River Reach Standards and Spatial Feature
Dictionary
Facility ID Code
Content Standard for Cu/teral and Demographic
Data
Metadata
Completed public review:
Catlas~al Content Standard
Federal Domain of Values for Data Content Standard
Cadastral Collection Standard (Cadastral)
Clearinghouse Metadata Proftle (Cadastral)
Classification of Wetlands and Deepwater Habitats
of the United States
Source: Federal Geographic Data Committee Newsletter~ November 1995.
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