The standard DEM consists of a regular array of elevations cast on a designated coordinate projection system.
Coverage is for the United States.
The US EPA 1-degree DEM shapefiles are polygonal representations of the original USGS DEM raster files resampled to a 300m x 300m cell size. The buffered CUs were used to clip corresponding areas from the DEM raster files. Two attribute fields were added to each shapefile's database component to represent elevation in both meters and feet.