Creating shaded relief directly from seamless DEMs can be problematic, because the horizontal units are in decimal degrees but vertical units are in meters.
The area of coverage of any particular 3DEP DEM product is generally determined by the availability of source elevation data of similar or higher resolution.
A digital elevation model, or DEM, is a representation of the terrain (bare-earth) with elevations at regularly spaced intervals.
The 5-meter DEMs in Alaska contain ‘DTM’ in the file names.
The laser pulses emitted from airborne lidar systems may be reflected from man-made structures, vegetation, or the earthen surface.
The most recently published figure of overall absolute vertical accuracy of the seamless DEMs within the conterminous United States, expressed as the root mean square error (RMSE) of 25,310 reference points, is 1.55 meters.
There are two types of metadata available for 3DEP products: (1) spatial metadata, and (2) FGDC metadata. Spatial metadata in the form of a shapefile is supplied as a part of each product download, or may be obtained at the
3DEP DEMs can be ingested by many commercial GIS software. The user will need to review specific software for compatibility.
3DEP standard DEMs are produced from the highest quality elevation sources within the holdings of the USGS National Geospatial Program. As of 2015, about 25% of the conterminous U.S.