Digital Elevation Model (DEM)

DEM map of Salt Lake City West, Utah

DEM uses Geographic Information System (GIS) technology to create, manipulate and analyze spatial data. A digital elevation model (DEM) is a digital representation of ground surface topography or terrain. It is also widely known as a digital terrain model (DTM). A DEM can be represented as a raster. DEMs are commonly built using remote sensing techniques, however, they may also be built from land surveying. DEMs are used often in geographic information systems, and are the most common basis for digitally-produced relief maps. Digital elevation models may be prepared in a number of ways, but they are frequently obtained by remote sensing rather than direct survey. The quality of a DEM is a measure of how accurate elevation is at each pixel (absolute accuracy) and how accurately is the morphology presented (relative accuracy).
http://edc2.usgs.gov/geodata/images/saltlake.gif