Geostatistical Analyst extension to ArcGIS offers 11 models. The other reason is the lack of a standardized procedure for comparing the models. Webster and Oliver (2001) recommend a procedure that combines visual inspection and cross-validation. Cross-validation, as discussed later in Section 15.5, is a method for comparing interpolation methods. Others suggest the use of an artificially intelligent system for selecting an appropriate interpolator according to task-related knowledge and data char acteristics (Jarvis, Stuart, and Cooper 2003)