A DEM (digital elevation model) is digital representation of topographic surface with the elevation or ground height above any geodetic datum. Various types of DEM are already described in 2-8 and Figure 2.11 of Chapter 2, Volume 1 as well as in 2-4 and Figure 2.13 ~2.15 of Chapter 2, Volume 2 including grid cell surface, TIN (triangulated irregular network), contour lines and profile.
Figure 3.1 shows three major DEMs that are widely used GIS.
A DTM (digital terrain model) is digital representation of terrain features including elevation, slope, aspect, drainage and other terrain attributes. Usually a DTM is derived from a DEM or elevation data. In this book, a DEM refers to a model with elevation data in digital format by which elevation at an arbitrary location in the area can be interpolated, while a DTM refers to terrain features in digital format, that can be derived from the elevation data.Figure 3.2 shows several terrain features including the following DTMs.
Slope and Aspect
Drainage network
Catchment area
Shading
Shadow
Slope stability
