(n) A 3-D computer model of a land form generated from survey data. Such models are often used by civil engineers and land planners to explore possible placements of structures or changes to the terrain before actual construction begins.
Digitally encoded information about the elevation (or variation of relief) of a given area. This gives a quantitative model of landform. Often the terms DEM (Digital Elevation Model) and DTM (Digital Terrain Model) are used interchangeably, although many prefer to use the term DEM to describe a model containing only discrete data on elevation.
A topographic surface or computer representation of terrain stored in a digital data file as a set of 3-dimensional ("x,y,z") coordinates. The image may be displayed on a computer monitor or portrayed on a map. Also called a digital elevation model (DEM).