- The paper presents a GIS model for mapping soils in the semi arid region of Israel. The model is based on a priori knowledge of the soil generating factors in the study area, namely (1) the parent?material (lithology) which determines the origin of the soil; and (2) the relief (including the drainage patents) which is responsible for erosion, deposition, and leaching processes along the catena. A special attempt was made to represent soil belts in small subwatersheds with different parent?material. The width of these belts can be varied as a function of the local relief. We believe that GIS techniques, in contrast to conventional survey and mapping methods, have the potential to overcome the manpower and fiscal restrictions which limit monitoring of large areas and areas which are for different reasons difficult to access. However, systematically generalizing a spatial model for a large area may introduce some errors, either due to local variations which were not taken into account, or regional variations.