DEM

 

http://www.geo.cornell.edu/geology/classes/Geo101/fallck/deglaciation.html

A digital elevation model (DEM) is a digital model or 3D representation of a terrains surface created from terrain elevation data. They consist of a sampled array of elevations for a number of ground positions at regularly spaced intervals. The model above shows the deglaciation of the Cayuga Lake Basin.