With the increasing availability of SAR satellites (ERS1, ALMAZ, J-ERS, RADARSAT) along with optical remote sensing platforms (LANDSAT, SPOT), it is critical to be able to register, compare and analyze data from different sources. In this paper we will show how DEM can be used to help in these various processes in particular for SAR imagery. DEM as well as orbitographic data along with the sensor description are required to generate terrain geocoded registered products. In the case of SAR imagery these 'ancillary data' can also be used to generate by-products such as overlays, shadows, compressions and dilatations thematic maps. These maps will help in further analysis and resampling of the SAR data. Applications for improved SAR terrain geocoding as well as special radar products, SAR image interpretation and SAR interferometry will be described.