Digital Elevation Models (DEM) for earth science studies, particularly over large areas, can be obtained via remote sensing instruments using optical and radar sensors at low costtime and with a variable resolution. However, since the reliability of the geomorphometric analysis asks for the accuracy of the DEM used, in this paper we offer a description of the main sources of spaceborne systems for DEMs generation as well as a brief analyses of two DEMs like those produced from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery (optical) and from Shuttle Radar Topography Mission (SRTM) data (radar), through a direct comparison in terms of altitudinal classes and first order topographic derivatives, such as slope, aspect and shape. Finally a gallery of the imagery computed is attached.