Data Layer: TRANSPORTATION (DLG)
You are invited to read the definitions of terms used in this data standard.
||Transportation Data (DLG)|
||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.|
||USGS EROS Data Center is the source for 1:100,000-scale data in DLG format.
SDTS information for USGS data available in SDTS format.
|Historical Data||For information on past versions of this standard, contact the National Data Administrator, Geospatial and Data Services, Division of Information Resources and Technology Management.|
Part 270, FW 6, Data Management and Standards, has been superceded by Part 274, FW 2, Establishing Service Data Standards.
USGS DLG Data - product description, prices, sample data, search and order DLG data.
DLG Standards - this site includes links to DLG documentation, selectable by scale at the site; very large documents.
The SDTS Information Site - includes documentation, FAQ's, and data pointers.
||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.
Spatial Data Transfer Standard (SDTS) - 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 Public Domain Software for Use with USGS Geographic Data page for notes on all DLG data.
||January 14, 1999|
||January 28, 2011|
||Chris Lett, National FWS GIS Coordinator, Geospatial and Data Services, Division of Information Resources and Technology Management.|