When a normal vector of slope surface ("surface vector" here) is shown as a point on a Wulff's net overlaying the basal plane of the HSI color cone, the vector is displayed by a color on a map. Accordingly, this map shows spatial distribution of surface vectors, each of which represents a slope direction and a slope degree at a point. The surface vector map is very useful to extract geomorphological features such as faults, linear structures, ring structures and others. If a stereo-pair of a surface vector map showing topography is provided, characteristic geomorphologies are extracted easier.