Digital Line Graph
Digital Line Graphs (DLGs) are digital vector representations of cartographic information derived from USGS maps and related sources.
Depending on scale, the following layers (or categories of feature type) may be available:
|Public Land Survey System (PLSS)||Township, range, and section lines|
|Boundaries||State, county, city, and other national and State lands such as forests and parks|
|Transportation||Roads and trails, railroads, pipelines and transmission lines|
|Hydrography||Flowing water, standing water, and wetlands|
|Hypsography||Contours and supplementary spot elevations|
|Non-vegetative features||Glacial moraine, lava, sand, and gravel|
|Survey control and markers||Horizontal and vertical monuments (third order or better)|
|Manmade features||Cultural features, such as building, not collected in other data categories|
|Vegetative surface cover||Woods, scrub, orchards, and vineyards|
DLGs are available in Optional format, written as ANSI-standard ASCII characters in fixed-block format.
The USGS produces three primary types of DLG data:
- Large-Scale (7.5-minute) DLGs correspond to the USGS 1:20,000-, 1:24,000-, and 1:25,000-scale topographic quadrangle maps. They are primarily cast to the Universal Transverse Mercator (UTM) projection system, but some are cast to the State Plane coordinate system. They are referenced to either the North American Datum (NAD) of 1927 (NAD 27) or the NAD of 1983 (NAD 83). The files are available in Optional and Spatial Data Transfer Standard (SDTS) format. Optional format is distributed on CD-ROM, DVD, and File Transfer Protocol (FTP). SDTS format is distributed via FTP download.
- Intermediate-Scale (1:100,000-scale) DLGs are derived from USGS 30- by 60-minute quadrangle maps. The following products are available:
- Individual 1:100,000-Scale DLGs are sold in 30- by 30-minute units that correspond to the east or west half of USGS 30- by 60-minute topographic quadrangle maps. Each 30-minute unit is produced and distributed as four 15- by 15-minute cells. They are cast to the UTM projection system and are referenced to either NAD27 or NAD83. The files are available in Optional and SDTS format. Both formats are distributed on CD-ROM, DVD, and via FTP download.
- 1:100,000-Scale Hydrography and Transportation CD contains 30- by 60-minute quadrangles for the hydrography and transportation layers only. Fourteen sectional regions in the United States covering the conterminous 48 States and Hawaii are available. Each 30-minute unit is distributed as four 15- by 15-minute cells. They are cast to the UTM projection system and are referenced to either NAD27 or NAD83. Available in Optional format and distributed on CD-ROM.
- Small-Scale (1,2,000,000-scale) DLGs are derived from the USGS sectional maps from the U.S. National Atlas. The following products are available:
- 1:2,000,000 State DLGs (Current Data) contain files that date between 1990 and 1994. The files are organized on a state-by-state basis, and include the conterminous U.S. and Hawaii. Alaska is not available. They are cast to Albers Equal-Area conic projection. 1:2,000,000 State DLGs are available in Optional and SDTS format. Optional format is distributed on CD-ROM. SDTS format is distributed via FTP download.
- 1:2,000,000 Section DLGs (Historical Data) contain files that date between 1973 and 1980. The U.S. and Hawaii are divided into 21 regional sections. The files are distributed on CD-ROM and each CD will include Optional, Standard, and Graphic formats. Optional format is cast to the Albers Equal-Area conic projection. Standard format is cast to the Cartesian coordinate system. Graphic format is expressed in geographic coordinates (latitude/longitude).