DLG (Digital Line Graph)

http://weather.unisys.com/usgs/3sec/index.php

According to the U.S Department of Interior and the U.S Geological Survey Fact Sheet, "Digital line graph (DLG) data are digital representations of cartographic information. DLG’s of map features are digital vectors converted from maps and related sources. The U.S. Geological Survey (USGS) DLG data are classified as large, intermediate, and small scale." The map above features digital elevations of the United States, which each color representing difference elevation levels.


Source: http://egsc.usgs.gov/isb/pubs/factsheets/fs07896t.pdf