 The US Geological Survey produces the National Elevation Dataset, a seamless DEM for the United States, Hawaii and Puerto Rico based on 7.5' topographic mapping.As of the beginning of 2006, this replaces the earlier DEM tiled format (one DEM per USGS topographic map).OpenTopography is a U.S.-based community access source of a large amount of high-resolution topography data for the U.S.