File > Import > Surface > DEM - "Invalid DEM file '<path to file>'. Only 7.5 minute data accepted."
This command requires that the DEM data is in 7.5-minute topographic quadrangles.
The United States government has collected digital terrain model data (x,y,z) information for most of the continental United States. The majority of this data has been collected in a grid pattern, with a grid cell size of 30 by 30 meters. This information, known as Digital Elevation Models, or DEM data, is available from the U.S. Geological Survey for a small fee.
DEM data offers an inexpensive means to model areas where more detailed data collection techniques have yet to be performed. However, this command is not well suited for detailed engineering analysis due to the limited precision of the data contained in these datasets.