Tools for electromagnetic simulation, such as SPECRAY EM / FERMAT, a jointed development of OKTAL SE company and French ONERA EM research centre, are well adapted to RCS or ISAR image computations down to millimetre wavelength for high realistic targets described using detailed CAD files. Moreover, this type of tool can be efficiently used in order to compute the same RCS of targets but taking into account the close environment, i.e. the clutter of this target, in the same run. Besides, it is possible to use the same type of tool in order to compute a complete reflectivity map of the terrain, including targets, that can be a very nice input of SAR treatment models. The basic problem is the terrain modeling. OKTAL SE company has developed the AGETIM terrain modeling tool, with the support of ANVAR, DGA and CELAR in France. This tool enables to automatically generate a 3D terrain mesh including complete modeling of features like roads, rivers or forests. This "terrain CAD file" is enhanced with physical attributes at polygon or texture level, which enables to perform EM ray tracing computations in order to provide a virtual stimulus to SAR imagery models. This paper intends to present the whole process from geographical data to SAR reflectivity map.