U.S. Fish & Wildlife Service

Data Layer: TRANSPORTATION (DLG)

You are invited to read the definitions of terms used in this data standard.

Name
 Transportation Data (DLG)
Description
 The data consists of digital maps created by the U.S. Geological Survey (USGS) that depict transportation items such as roads, railroads, and pipelines. Although these data now exist in Spatial Data Transfer Standard (SDTS), as well as Digital Line Graph (DLG) format, they are still called DLG data. The data are available on the Internet, free-of-charge, or on inexpensive CD's. The CD's contain 1:100,000- and 1:2,000,000-scale data in DLG format, available nationally. The 1:24,000-scale data on the Internet  is available only in SDTS format. While it is not yet completed nationally, work is in progress. 
Source
 USGS EROS Data Center at http://edc.usgs.gov/geodata/ is the source for 1:100,000- scale DLG format data.
SDTS information is at http://mcmcweb.er.usgs.gov/sdts/data.html for USGS data available in SDTS format.
Reference(s)

Part 270, FW 6, Data Management and Standards, dated September 30, 2002.

USGS DLG Data information is found at http://edc.usgs.gov/products/map/dlg.html. This includes a section on SDTS data, as well as DLG optional data.
The Data User's Guide is available from http://geography.usgs.gov/standards/. Complete DLG documentation, selectable by scale at the site; very large documents.
Transportation Attribute Coding is found at http://www.fws.gov/data/gisconv/trans.zip. This updated document on the attribute codes gives a detailed definition of each code and describes how they were created. It is in WordPerfect 5.1 format, zipped with PKZip. A complete set of this updated documentation for DLG data is also available at the Data User's Guide site referenced above, in the dlgstnds subdirectory.
The SDTS Information Site is at http://mcmcweb.er.usgs.gov/sdts/. This site includes documentation, FAQ's, and data pointers.

Use Instructions
 The USGS Transportation data layer in DLG format should be used wherever it is available in an appropriate scale and with current information. Alternative data may be needed if the USGS data is old, not in the appropriate scale, or lacking in detail.

There are several alternative sources for roads data that are currently in use, including Census Bureau TIGER data or data derived from the TIGER files. The Wessex roads data is an example of derived data. Depending on the geographic location or intended use, these files might be more useful than the DLG data. They frequently contain more information in urban areas. The TIGER data, for example, contains address geocoding. Generally, however, the DLG data will be the only source for railroad and other miscellaneous transportation information.

Transportation data is generally used as a reference GIS layer, but may be used in analysis as well, particularly for siting other facilities. Tools for utilizing this data are listed below.

Limitations: Data should always be used at the scale appropriate to the application. The USGS makes every effort to achieve a high level of accuracy in all of its published products. An important aim of its accuracy control program is to meet the U.S. National Map Accuracy Standards. These standards vary with scale; for example, 1:24,000-scale data will be much more spatially accurate than data at the 1:100,000-scale. If the degree of precision is very important to the application, check the above reference to make sure the data being used are appropriate.

Tools
 Transportation attribute data can be found at http://www.fws.gov/data/gisconv/dlgtrans.zip. These are files containing a list of the attribute codes in Dbase III file (dbf) and WordPerfect 5.1 (textual) format, zipped with PKZip. The codes have the same descriptions in both files when they are present in both files. The dbf files contain only codes currently in use. The WordPerfect document also contains older or deleted codes displayed in italics within parentheses.

Multiple Dbase files are included. One file, dlgtrans.dbf, contains all the attribute codes. The others, dlgtrnrd.dbf, dlgtrnrr.dbf, and dlgtrnmt.dbf contain only the codes, respectively for roads and trails; railroads; and pipelines, transmission lines, and miscellaneous transportation features. See the readme.trn document zipped with these files for more details on the fields contained in the Dbase files.

SDTS Conversion Overview - There are some tools now available to convert transportation data in SDTS format into other formats. The SDTS tools are undergoing further development, and new tools will be posted when they are ready.

Visit the Documentation and Tools for Utilizing USGS DLG Data page for notes on all DLG data.

Phase
 Adopted
Approval Date
 January 14, 1999
Validation Date
 January 3, 2005
Data Steward
 Deb Southworth Green, National FWS GIS Coordinator, Branch of Data and System Services, Division of Information Technology Management

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These pages are maintained by the U.S. Fish and Wildlife Service, Division of Information Technology Management. Please feel free to contact Deb Southworth Green with any questions and comments.

Keywords=fish, wildlife, animals, birds, data, standards, elements, layers, transportation, dlg
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