|
Spatial Data and Geographic Information Systems Within the Bureau of Transportation Statistics
October 3, 1994 SPATIAL DATA AND geographic INFORMATION SYSTEMS WITHIN THE BUREAU OF TRANSPORTATION STATISTICS (BTS) An important driving force in BTS data compilation and analysis activities is the need for extensive geographic data on transportation facilities and networks. the activities they serve, and the surroundings they affect. The emphasis on geographic data and analyses reflects the central purpose of transportation: to connect, separate locations and accommodate the flow of people and goods. This requires refinement and application of analytical methods based on geographic information systems (GIS) technology. GIS provides a practical and realistic method for measuring and understanding' the extent, use, performance and consequences of the transportation system. This paper presents a plan to identify and obtain the required information to support a GIS structure, integrate this information into cohesive tools necessary to support planning and policy initiatives, and make the information available for use by the public and other agencies. Overview BTS is compiling a geographic database to support research, analysis, and decision making across all modes of transportation. The database is designed primarily to meet the needs of DOT at the national level, but will have major applications at State and local scales throughout the transportation community. Most of the database is to be published as a National, Transportation Atlas, including base maps that portray the extent and connectivity of the nation's, transportation system, thematic maps** that portray the use, and consequences of transportation, and electronic files that are used to develop the maps and analyze transportation networks. The remaining part of the database will be ___________________ . This paper was prepared by Kathlien L. Hancock, Vanderbilt University,, for the Center for Transportation Analysis, Oak Ridge National Laboratory, and the Bureau of Transportation Statistics, U. S. Department of Transportation. Comments on this paper are welcomed, and should be directed to Dr. Hancock, Box 1625 Station B,.Nashville, TN 37235 (voice: 615-322-2720; fax: 615-322-3365) or to Rolf Schmitt, Bureau of Transportation Statistics, U.S. Department of Transportation, Room 2104, Washington, D.C. 20590 (voice: 202-366-DATA; or fax: 202-366-3640). .. A thematic map is a map that displays one or more specific types of information usually using symbols to represent different classes or movements of information. 1 October 3, 1994 used for internal BTS analyses, but will be left to others to publish as shown in Figure 1. The National Transportation Atlas database is organized into four layers. of information. The facilities, layer represents the location, physical characteristics, and connectivity of highways, railroads, waterways, fixed guideway transit, airports, pipelines, terminals, bridges, locks, structures. The service layer represents transportation services on and across the transportation facilities, such as bus lines and railroad trackage rights. The flows layer represents interactions between areas, such as commodity movements and donor-donee financial relationships, which are assigned to specific transportation facilities and services primarily with analytical models. Much of the flow data will come from the American Travel Survey and the Commodity Flow Survey, both of which are being conducted by the Bureau of the Census for BTS, and from the Census Transportation Planning Package of journey-to-work data that was published on CD-ROM by BTS. Finally, the background layer includes data of use to the transportation community that are published and maintained by others. Examples include political boundaries, geographic names, population distributions, economic activity, and environmental conditions. Boundary and name files that help define locations for the facility, service, and flow layers are to be published in the National Transportation Atlas. The remainder of the background layer is used by BTS for creating thematic maps and preparing analyses, but is left to other agencies for dissemination. Consecutive to this work is a national attempt to modernize the Nation's mapping programs through interagency and intergovernmental cooperations under Executive Order 12906, Coordination of Geographic Data Acquisition and Access: the National Spatial Data Infrastructure (NSDI). Under this order, DOT has responsibility for the transportation layer of the NSDI. NSDI coordination is provided by the,.Federal Geographic Data Committee (FGDC), on which BTS sits for DOT (the only representative of both the transportation and statistical communities). NSDI provides basic location (but not necessarily connectivity) data for the facilities layer of the National Transportation Atlas through the Census Bureau's TIGER files and the Digital Line Graphs (DLGs) of the U.S. Geological Survey; BTS provides updates on location and assures adequate representations of connectivity for facilities of potentially national significance that appear on the NSDI transportation layer as shown in Figure 1. 2 Click HERE for graphic. Figure 1. Schematic of BTS Spatial Data 3 October 3, 1994 Contents of BTS Geographic Data Bases Table 1 summarizes, the proposed databases that will be included as part of BTS spatial data. As other information and databases are identified they will be integrated into the overall framework by BTS. BTS spatial data consists of two classes of data, information used in the National Transportation Atlas and information from sources outside the Department of Transportation for use within BTS and the Department. Figure 1 presents a schematic representation of the BTS spatial data. The National Transportation Atlas databases will be disseminated to the public. Information used exclusively within the Department, while' available to the public upon specific request, will be maintained within BTS. Version 1.0 of the National Transportation Atlas databases, which emphasizes location and connectivity information, will be available in the first -quarter of Calendar Year 1995. Later versions will be released as considered appropriate by BTS. Spatial Representation Spatial data within.the Federal Government have been generated at different mapping scales. Table 2 summarizes these scales and lists examples of recommended.uses at each scale. Click HERE for graphic. The databases used. by BTS have been created by different agencies within the Federal Government. In general, the networks have been made available at two scales; 1:100,000 and 1:2,000,000. ______________________ Root-mean square positional accuracy. 4 Click HERE for graphic. October 3, 1994 As shown in Table 2, the 1:2,000,000 scale networks are used for national level planning and analysis functions, while, the 1:100,000 scale networks are used for more localized activities at the, state, regional and metropolitan level. The primary reason for this distinction is the increased size and detail required for the 1:100,000 scale networks, which directly affects the time and resources required to perform planning tasks. Currently, the 1:100,000 and 1:2,000,000 modal networks are published as two separate databases. Ultimately, BTS plans to maintain only the 1:100,000 network databases and to provide a utility to decrease (or thin) the size of each network to replace the current 1:2,000,000 networks for national applications. Attributes Two types of attributes have been defined for the National Transportation Atlas databases: locational information, and transportation attributes. Locational attributes provide information necessary to represent the data spatially, to uniquely identify every element in the databases, to provide connectivity of transportation facilities and services, and to provide referencing systems for transportation attributes. In general, these attributes will be located in a single database.* Tables 3 through 10 present proposed attributes for facility network link, facility network node, facility terminal and other structures, service network, flow layer point, line, boundary, and area databases, respectively. Facility network nodes and facility terminals are located in separate databases. Nodes are components of networks (generally, where two links intersect) and are not necessarily terminals. Similarly, terminals are probably not located at a given node although they will be referenced to the nearest node on the appropriate network. Note that the locational attributes will probably consist of, or include, the National Spatial Data Infrastructure (NSDI) core attributes, which have not yet been formalized. Transportation attributes consist of information used for planning and analysis. These attributes will probably be maintained in several databases and will be identified from specific analysis requirements and by the availability and quality, of the desired data. Tables 11, 12 and 13 provide summaries of representative transportation attributes for network links, nodes, and terminals, respectively. If already available, transportation attributes will be included in Version 1.0 of the National _________________________ * For the modal networks, each database may consist of one or more files that have link, node and geometry information. 6 Click HERE for graphic. Click HERE for graphic. 7 October 3, 1994 Click HERE for graphic. Click HERE for graphic. 8 October 3, 1994 Click HERE for graphic. Click HERE for graphic. Click HERE for graphic. Click HERE for graphic. 9 October 3, 1994 Click HERE for graphic. Click HERE for graphic. Click HERE for graphic. 10 October 3, 1994 Transportation Atlas databases. Otherwise, BTS will evaluate the use, availability and probable quality of desired transportation attributes to determine the priority for acquiring the information. International Extension With enactment of the North American Free Trade Agreement (NAFTA) and growing interrelationships of U.S. domestic-transportation and international trade, BTS databases must be expanded beyond the' U.S. borders' The Federal Railroad Administration (FRA) has extracted the rail networks for Mexico and Canada from the 1:1,000,000 scale Digital Chart of the World. Information on border crossings and customs locations is also being compiled. The next step for BTS and other agencies is to extend this-work to the highway and waterway networks and terminals throughout North America. As these become available, they will be incorporated into BTS databases. Only limited quality control will be performed on these networks. Compilation of National Transportation Atlas Databases BTS is performing several major tasks to compile and make available the National Transportation Atlas databases: . Assembling identified source materials, . Resolving locational differences (planimetric) . Checking for connectivity within modal networks . Adding available attributes to existing databases, and, . Linking databases together. Table 1 lists the source agencies for each database. Of the three principal modal networks, the highway network database consists of approximately 400,000 miles of highways, or 10% of the total roads in the United States. The rail network contains the entire mainline and secondary rail systems while the waterway network includes all navigable waters. For 1: 100,000 scale, these networks were developed as follows: the highway[2] and rail[3] (and fixed transit) databases were each combined from the 1:100,000 DLGs[4] and for rail, the Bureau of Census TIGER/Line files,[5] supplemented in the case of highways by State-supplied urban area maps. The waterway database was combined from digitization of Navigation Charts used by the U.S. Coast Guard and USGS quad maps.[6] The pipeline network at the 1:100,000 scale has not yet been initiated. As these databases have been developed, the issue of planimetric accuracy (how the information is represented in two dimensions) has become important. Figure 2 provides an example of the rail network in 11 Click HERE for graphic. Figure 2. Example of Rail Networks for Downtown Chicago 12 October 3, 1994 downtown Chicago from the two DLG sources (1:2,000,000 and 1:100,000) and the TIGER/Line files (1:100,000). As can be observed the planimetric accuracy and completeness of the information vary across different sources. DLGs have greater planimetric accuracy for older facilities particularly with respect to shape points along a network link. TIGER is more current, particularly for the street network, but often at the expense of planimetric accuracy. The NHPN and 1:2,000,000 rail databases have the transportation attributes, but lack the locational precision of either TIGER or Census DLGS. BTS must reconcile the differences and capture the best of each source. Quality of information is very important to BTS. To ensure the quality of the data in the NTA BTS will perform network connectivity and other data checks as outlined in the following section. Information currently available for the NTA is primarily locational in nature. To increase the usefulness of the NTA databases, additional attributes must be collected or obtained from other sources such as the Highway Performance Monitoring System (BPMS). These attributes must then be "snapped" (added) to the existing databases or overlayed onto the networks and facilities. BTS will continue to add this information as it is identified. In many cases, attribute information becomes available on a state by state or regional basis. Generally, BTS will establish an attribute code in the appropriate database indicating not yet available". As the,information for that attribute is obtained, the code will be updated. In this way, the National Transportation Atlas databases will contain the most current information but will not lead users into misunderstanding attributes. Because the flow of people and goods is usually intermodal, BTS will incorporate specific connections between networks and terminals. initial connections include direct node and link references within the terminal databases. Currently those databases include only the major airports, rail/highway terminals, water ports and transit stations. As intermodal analyses increase, BTS will expand the number of terminals to reflect the needs of the analyses. Data Quality Control BTS will perform very specific quality checks on the information Control included in the spatial data framework. These checks will include planimetric consistency, completeness of data elements and connectivity Of the transportation networks. Initially, the databases will be overlayed on each other and checked for planimetric consistency. The networks will be checked for overlap on boundaries and each other. Boundary and terminal locations will be 13 October 3, 1994 checked against state maps. If discrepancies are identified, the appropriate USGS quad map will be,consulted. For databases over which BTS controls maintenance, incorrect information will be corrected and identified in the metadata files or other appropriate locations as being modified. For databases maintained by other agencies, the discrepancy will be documented and forwarded to the appropriate agency. A list of such discrepancies will be maintained in the spatial data framework documentation. As corrections are made or disputed by the appropriate agency,, the list will be updated to reflect the action taken. Each of the data elements within each database will be checked for completeness. The percentage of blank, records for each element will be reported in the spatial data framework documentation. If an element has a flag or indication for "unknown", "not yet identified", or a similar identifier, records with this flag will be included in the reported percentage. This information will be updated as each version of the corresponding database is released. As appropriate, standard GIS software will be. used to display different attributes across a network to identify obvious discontinuities within that attribute field. For example, the different categories of highway functional classifications will be highlighted in different colors. Sections of highway that have a discontinuous link (i.e. a link,appears red with yellow links on either side) will be noted as having a discontinuous attribute. All such variations will be noted and addressed as discussed above. Initially, this will not be an exhaustive test and will be used for regional checks. Networks will be evaluated for connectivity, circuity, and reasonableness using sub-network identification and flow-based routing. The National Commodity Flow Survey and other current projects using, databases from the National Transportation Atlas databases will provide actual routing and connectivity checks. Any discrepancies from these activities will be identified and corrected as discussed above. As additional capabilities are obtained and/or developed by BTS, more advanced network checking will occur. As the National Transportation Atlas and associated databases are released.to the public, a form will be included in the documentation requesting notification of inconsistencies or incorrect information identified by users of the Atlas along with user-defined corrections. Corrections to the databases will be handled as described above. The BTS is currently in the process of developing a formal quality control procedure that will provide and discuss more comprehensive 14 October 3, 1994 evaluation measures. BTS will also establish a clearinghouse either inhouse or through one of its GIS partners to coordinate the collection, incorporation, and dissemination of collections with the user community. Maintenance The information within each of the databases will be maintained by the appropriate agency as specified in Table 1. BTS will maintain selected transportation attributes that are not maintained by another agency and will support other efforts as requested. Maintenance will include correcting information identified under quality control activities, updating and/or adding information as it becomes available, including new use layer information, and maintaining the databases in ASCII as well as existing GIS software formats. Modifications will be documented in an audit field to identify whether the change occurred because of corrections to data' or additions to the database. This is important for comparison studies where using corrected information for previous versions of the NTA is necessary to provide a valid comparison. As modifications are made to the databases, the documentation and metadata files will be updated to reflect these modifications. BTS will also remain in contact with other agencies to ensure that the databases within the BTS spatial data are the most current versions. Archival BTS will maintain archival copies of all information used in the BTS spatial data framework, including the National Transportation Atlas, and for any analysis performed by or for BTS. These archival copies will be maintained on permanent read-only storage media, such as compact disc, and will be identified by version number or by analysis name and date. For example, all data, programs, and documentation used for the 1993 Commodity Flow Survey will be archived by date and study name. These archival files will be catalogued and maintained at the BTS GIS laboratory. Integration and Analysis Tools With widespread availability of commercial geographic information systems software, many tools and applications are commercially available. Whenever the needed capabilities are accessible through vendors, BTS will acquire this software. If necessary, BTS will develop tools and will make the technologies available to other interested users. 15 October 3, 1994 Examples of these tools include: . Geographic Data Visualization Tools: - user selected multi-dimensional tabulations - chloropleth maps - flow maps . Network Simplification-Tools: - link chaining (i.e. end-on link collapsing) - network spur removal (i.e. removing dead-ends) - sub-network selection - network aggregation (i.e. merging of two or more parallel routes) . Network Matching Tools. BTS is also developing a GIS Center within the Department of Transportation headquarters. The goals of this center are to: . integrate geographic data products for publication and use by.DOT, . prepare maps and other visual displays, analyze temporal and geographic variation in the extent, use, performance, and consequences of the transportation system, and . provide a "test bed" for the development and demonstration of GIS technology and geographic analysis methods for DOT and other users. Combining software and the GIS Center, BTS will have the necessary tools to provide integration and analysis support to the transportation community. BTS Products The mission of BTS is "to compile, analyze, and make accessible information on the Nation's transportation systems".[7] To meet this mission, BTS is actively developing products that disseminate this information to the public as indicated in Figure 1. For spatial data, BTS will make available two types of products: database files and both paper and electronic (displayed on a computer screen) maps. The database files can be used for analyses as well as generating maps and will be available as the National Transportation Atlas databases. The maps will be available as the National Transportation Atlas and as-thematic maps for use in BTS and Office of the Secretary of Transportation (OST) reports. Another product will be. any user aides and software tools, or their 16 October 3, 1994, corresponding procedures, developed by BTS for use with the Spatial data. These products may be in the form of computer software or technical reports. National Transportation Atlas Databases The BTS will provide annual compact discs of the National Transportation Atlas databases initially at two scales: 1:100,000 for local and regional purposes, and 1:2,000,000 for national evaluations. The discs will contain all associated databases in ASCII format, se corresponding documentation, and display and extraction software beginning with Version 1.0 in 1995. This version will contain location and connectivity information. Later releases will contain additional attributes. Subsequent versions of the National Transportation Atlas will.be numbered as follows. Updates to existing databases will be incremented by decimal, or 1.1. Major changes to existing databases (for example, a more detailed pipeline database) or addition of a new databases to the Atlas (service networks) will be incremented by new version numbers, or 2.0. Thematic Maps As required to support the Transportation Statistics Annual Report, the National Transportation Atlas. and other DOT initiatives, BTS will provide thematic maps of information from the spatial data framework and from analyses using the BTS spatial databases. Generally, these maps will be available in both raster and vector formats as well as on paper at 1:1,000,000 or 1:7,500,000 scale of detail. Conclusion Spatial data and GIS technology are as important as traditional statistics to BTS. Geographic and temporal variations must be understood to understand transportation issues. In support of this belief, BTS has committed to compiling, developing and maintaining a collection of databases that represent the current transportation system along with the necessary user aides to make this data available to the general public. This collection is generally referred to as the National Transportation Atlas databases and will be available to the public during the first quarter of Calendar Year 1995. BTS's goal is to provide data and analysis tools, but not turn-key solutions to transportation issues. 17 October 3, 1994 References 1. US GeoData Digital Line Graphs from 1:2,000,000-Scale Maps, United States Department of the Interior U. S. Geological Survey, Reston, Virginia, 1989. 2. The Federal Highway Administration is publishing and maintaining Version 2.0 of the National Highway Planning Network at a map scale of 1:100,000. 3. The Federal Railroad Administration has developed a 1:100,000 map scale rail network using the TIGER/Line files. FRA is currently updating and adding ownership and usage attributes to this network. Concurrently, Volpe National Transportation Systems Center is merging the TIGER/Line files with the Digital Line Graphs. 4. US GeoData Digital Line Graphs from 1:100,000-Scale Maps, United States Department of the Interior U. S. Geological Survey, Reston, Virginia, 1989. 5. Bureau of the Census, "TIGER/Line Census Files: machine readable data files", prepared by the Bureau of the Census, 1990. 6. A consortium of Government Agencies has contracted Oak Ridge National Laboratory and Vanderbilt University to generate a database of the navigable waterways. Version 1.0 is complete. 7. Introduction to the Bureau of Transportation Statistics, U.S. Department of Transportation, May, 1993. 18
