ABSTRACT
Spatial mapping usually involves the interpolation and/or extrapolation of point data across surfaces to depict conditions at all positions on the land surface. Depending on the rate of degradation, spatial maps only represent a situation within a certain accuracy for a limited period of time. Qualitative models derived from modifications of soil-landscape models are efficient means of extrapolating point data based on conceptual relationships between observations of the soil property or condition being mapped and easily observable landscape features. Topographic, geological, climatic and other maps at different scales, different kinds of remote sensing data, and descriptions on historic and current land use may all be useful to plan a soil degradation survey. Variograms may be fitted by one of the standard models available in geostatistical software, e.g., spherical, exponential, Gaussian, power, or linear models.
