What is a DEM?
A digital elevation model (DEM) is a digital representation of ground surface, also known as topography or terrain. This is also widely known as a digital terrain model (DTM). A DEM or DTM can be represented as a raster (a grid of squares) or as a triangular irregular network, also known as a wire frame and are commonly built using remote sensing techniques, however they may also be built using land surveying methods.