Abandoned polygons

When one or more source polygons does not intersect (at all) with the target polygons, data from these polygons will not be transferred to the target coverage. For count data, this situation introduces a discrepancy between the total of the source values and the total of the target values.

For example, normally, when all of the source polygons are intersected (even just a little bit) by target polygons, the entire contents of the source polygons will be transferred to the target coverage. So, if the attribute to be transferred is the number of farms in each polygon, then the total number of farms in the target coverage will be the same as the total number of farms in the source coverage. But, if one source polygon does not intersect with any of the target polygons, its number of farms will not be assigned to the target cover, and so the target coverage will contain fewer farms than the source coverage.

To determine which source polygons will be abandoned, calculate the 'subarea' value (by selecting a subitem and subitemvalue, setting the calc-subarea on, and processing some data). Source polygons with a zero subarea will not be assigned to the target coverage.