DTM is often used as a generic term for DSMs and DTMs, only representing height information without any further definition about the surface Other definitions equalise the terms DEM and DTM,or define the DEM as a subset of the DTM, which also represents other morphological elements.

There are also definitions which equalise the terms DEM and DSM.On the Web definitions can be found which define DEM as a regularly spaced GRID and a DTM as a three-dimensional model (TIN).[7] Most of the data providers (USGS, ERSDAC, CGIAR, Spot Image) use the term DEM as a generic term for DSMs and DTMs. All datasets which are captured with satellites, airplanes or other flying platforms are originally DSMs (like SRTM or the ASTER GDEM). It is possible to compute a DTM from high resolution DSM datasets with complex algorithms (Li et al., 2005). In the following the term DEM is used as a generic term for DSMs and DTMs.

DTM is often used as a generic term for DSMs and DTMs, only representing height information without any further definition about the surface

A DEM can be represented as a raster (a grid of squares, also known as a heightmap when representing elevation) or as a vector-based  (TIN). The TIN DEM dataset is also referred to as a primary (measured) DEM, whereas the Raster DEM is referred to as a secondary (computed) DEM. The DEM could be acquired through techniques such as photogrammetry, lidar, IfSAR, land surveying, etc. (Li et al. 2005). DEMs are commonly built using data collected using remote sensing techniques, but 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.

While a DSM may be useful for landscape modeling, city modeling and visualization applications, a DTM is often required for flood or drainage modeling, land-use studies, geological applications, and other applications.