Requirements: iGO 8.3 or higher, iGO Primo, iGONextGen, iGO amigo, Becker or any GPS with Windows Mobile, or Windows CE or any Android device.
Dem files give you the ability to show an overhead view of the map (with terrain colors and shading), where you can pin your desired destination. In 3D mode Changes the view into a truly spectacular viewpoint. In 2D mode it shows colored areas depending on terrain height. See the pictures.