Abstract: A system obtains agricultural attribute data from the field. The agricultural attribute data is classified into a plurality of spatially distributed regions across the field. Samples are obtained to provide a second set of agricultural attribute data. A subset of the second set of agricultural attribute data is associated, by georeferencing, with one class of the spatially distributed regions. The subset is subclassified into respective zones, as may be done by interpolation to define contours. The classification process operates without regard to data that is not in the subset but is also taken from the second set of agricultural attribute data, i.e., the subclassification ignores data in the second set that is georeferenced to classes other than the class associated with the subset. The subclassification is repeated for all classes. An agroproduct prescription map is prepared for the application of agroproducts to the respective zones.