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Digital Line Graphs Data Layer

Digital Line Graphs are digital representations of the features displayed on a U.S. Geological Survey topographic map. DLGs are provided by the USGS in numerous scales of which 1:24,000 and 1:100,000 are the most commonly used. They are separated into four primary layers: boundaries, transportation, hydrography (surface water), and hypsography (contours). The map features are attributed with a series of numeric major and minor pairs that correspond to a specific item listed in the accompanying user guide. Without extensive knowledge of the user guide, access and use of these data are cumbersome and inefficient. As a result, the SCDNR has added several descriptive attributes to the DLG files, such as feature type and feature name, to facilitate DLG usage. For more information about the major and minor codes used with these data see the USGS Guide.

 

Digital Line Graph Attributing & Enhancements

  1. Import spatial and attribute data.
  2. Attach ACODE and PCODE attributes to DLG coverage.
  3. Georeference to statewide TIC grid.
  4. Clean and build as double precision coverages.
  5. Major & minor categories equalized across basins.
  6. Major and minor codes reconfigured to hierarchial order to facilitate searches.
  7. Major and minor codes converted to English-equivalent attributes to create feature type.
  8. Road names added where indicated on topo map.
  9. Interstate, US, and state road numbers encoded where indicated on topos.
  10. Roads split by county such that all roads within a county can be retrieved.
  11. Pipe and transmission lines and airports split into appropriate layers and airports converted to polygons.
  12. Boundaries split into refuge, reservation, municipal, park or other layers and built into polygons. Specific attributes added and encoded.
  13. Hydrographic features encoded with feature type and name as indicated on topo maps.
  14. All layers edgematched to within National Map Accuracy Standards. USGS treats quads independently. They do not move features from their topo base location, but flag those that need correction. SCDNR moves those features not within NMAS to edgematch, generally to within 3 meters.
  15. First quality review & correct problems.
  16. Second quality review by management staff.
  17. Edit/correct problems.
  18. Third quality review by Data Base Administrator.
  19. Quad added to SCDNR GIS Data Base.

Example of Digital Line Graph data, Beaufort, SC

Digital Line Graph of Beaufort, SC

Download Available DLG Data

Data is available for download at no cost from DNR's GIS Data Clearinghouse. Refer to DNR GIS DNR Clearinghouse for availability.

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