The USGS is currently using the Spatial Data Transfer Standard (SDTS) format rather than the DLG format. 1:24,000, 1:1,000,000, and 1:2,000,000 scale United States base maps are available in SDTS format from the USGS. To download these updated files for use in MapViewer, go to www.usgs.gov. For a current link to these files, visit our web page www.goldensoftware.com and click the Useful Links option.
There are two types of SDTS files. The DEM (Digital Elevation Model) files contain elevation information. These files cannot be used in MapViewer, but they can be used to create maps in Golden Software's Surfer. The TVP (Topological Vector Profile) files contain information such as political boundaries, water bodies, hypsography, roads, and railroads. These files can be used in MapViewer as base maps.