allowed me to make time for this extra task. Most notable in this list of friends and family is my wife, Robin, who endured many lonely nights while I sat in the home office typing away. David A. Wheeler, city engineer for the city of Ocoee, Florida, also provided patient support by allowing me as much as two months at a time away from contract work in his office to write the book. They and numerous others had to experience my frequent response to a request to do something for them: “I can’t right now, I have to work on the book.”
Well, that task is finished. Only you can decide how well it was done. If you can find something in this publication that helps you solve a problem with transportation geodatabase design, then I guess it was worth it.
About the author
J. Allison “Al” Butler has worked for state, regional, and local transportation agencies during a 30-year career, focusing on the built environment and information technology. He has been an innovator in spatial database design, traffic engineering, planning policy, public utilities, and economic development, and has authored more than 75 published works in those fields. Mr. Butler played a key role in developing the GIS professional certification program and, with Dr. Kenneth J. Dueker, co-developed the Enterprise GIS-T database design. He is a frequent conference speaker and workshop instructor on a variety of topics, including highway safety, geodatabase design, agency management, and land use planning. Al Butler is a licensed contractor and a certified planner, mapping scientist, and GIS professional.
Introduction
• Building the agile geodatabase
Modes of travel can be quite different but all follow a conceptual structure consisting of an origin, a destination, a path between the two, and a conveyance to move along the path. Designing Geodatabases for Transportation tells how to design a geospatial information system to manage data about transportation facilities and services.
An enterprise geodatabase can help solve two common transportation challenges: the many origins, destinations, paths, and conveyances that may be present; and the need to specify locations along the facility. There is also the matter of facility suppliers usually being different from facility users. The facility user focuses on origins and destinations. The facility supplier is concerned about the many paths over which a conveyance travels and generally not about specific trips. A transportation agency provides the facilities to support travel. Shippers—those who have goods to deliver—define the origin and destination for their shipment. A shipping company supplies the conveyances and selects the paths to move the shipper’s goods from origin to destination. Each origin and destination must be accessible from a transport facility. A shipping company can select a path only where a corresponding facility exists. Railroads perhaps can be viewed as being both suppliers and users of transport capacity although some may operate over facilities they do not own.
Transport databases
Transportation data is often specific to the various modes of transport. Designing Geodatabases for Transportation addresses six modes: walking, bicycling, motor highways, public transit (buses and commuter rail), railroads, and navigable waterways.1 All six modes involve linear facilities supporting point-to-point travel for people and material goods. The nature of the facility supporting travel and the way it is used differs with each mode. Some facilities support multiple modes of travel. Highways and roads accommodate motor vehicles, pedestrians, and bicycles. Railroads support commuter trains, long-distance passenger travel, and freight movement. Ships travel navigable waterways that flow under highway and railroad bridges.
Points of modal connection are commonly known as terminals, depots, stations, stops, and crossings. The name “intersection” is usually applied to highways, but conceptually includes other points where facilities cross and interact, such as railroad switches, crossovers, and diamonds; rail-highway grade crossings; and limited-access highway interchanges. Transport systems also include places where facilities cross but do not intersect, such as at bridges, viaducts, and tunnels.
Geographic information systems (GIS) for transportation—GIS-T in industry shorthand—routinely deal with mode- and function-specific applications, each with its own geodatabase design. What is rare is a GIS-T geodatabase that goes beyond serving the needs of a single application. Such a geodatabase must accommodate the many segmentation schemes employed and the various linear and coordinate referencing systems available to show where the elements, conveyances, and characteristics of transportation systems are located. Designing Geodatabases for Transportation shows you how to construct such an enterprise multimodal geodatabase, although the ideas presented in this book can be implemented for a single mode.
A transportation geodatabase addresses concerns beyond facilities and the services that use them. For example, facility elements and characteristics are affected by projects and activities that construct, maintain, and remove elements of the transportation system. There are also traffic crashes, bus routes, train schedules, and shipping manifests to consider.
Transportation applications are much too diverse for this book to present you with a complete transportation database design. That task is up to you. ESRI has successfully worked with user groups to develop a number of industry-specific data models. That approach will not work with transportation, which lacks a single, all-encompassing view of the industry due to its diversity. Not only are there modal differences to consider, but there are also differences in detail and abstraction. A trucking company, a city public-works division, and a state department of transportation (DOT) all need data about highways, but for their own purposes that require them to adopt very different data models. Even within a single transport agency there may be several different application-specific data models.
What this book offers is a collection of ideas and geodatabase design components to help you construct a model that serves your agency and its unique set of applications. It shows you a variety of ways to handle a specific data need, describing the pros and cons of each choice. In this way, Designing Geodatabases for Transportation provides a cafeteria of design options rather than a fixed menu to solve the broad range of transportation spatial data requirements.
Data models
Geodatabase design is normally expressed through a data model, which is a graphical way of describing a database. A data model is essentially a set of construction plans for a database. Some data models are very conceptual, others extremely detailed. Fortunately, all data models use a few very simple symbols. You need no prior experience with data models or geodatabase design to understand and apply the suggestions in this book.
All geodatabases form a set of abstract representations of things in the real world. The process of
