DEM, Digital Elevation Model, is a digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals. It is in raster format, so the cartographic dats is recorded, stored and processed in a cell or pixel. DEM's are georeferenced, meaning their features are tied into a coordinate system, datum, and map projection and reference specific locations (i.e. latitude & longitude) in space.
DEMs are commonly built using remote sensing techniques, however, they may also be built from land surveying. DEMs are used often in GIS, geographic information systems, and are the most common basis for digitally-produced relief maps.
Above you will see a DEM for Honolulu, HI. Note the use of shading to illustrate increasing elevation. The lowest level of elevation starts out with the dark shades of green, gradually lightening through shades of yellow, brown and white to represent those areas of higher elevation.
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