Difference (Spatial)

The spatial difference operation (also called erase or clip-inverse) computes the geometric subtraction of one feature layer from another. The output retains only the portions of the input features that fall outside the erase or subtraction features. Attributes from the input layer are preserved, while the areas covered by the erase layer are removed.

Difference takes two inputs: the features to be modified (input layer) and the features to subtract (erase layer). The operation clips the input layer along the boundaries of the erase layer and discards the overlapping portions. The resulting features retain the attributes and geometry of the input layer, minus any area that coincided with the erase layer. Symmetric difference, a related operation, returns areas unique to each input layer, excluding the overlap.

Environmental analysts subtract developed land from habitat maps to identify remaining natural areas. Urban planners erase existing park boundaries from a city extent to find underserved areas lacking green space. Transportation planners remove existing service coverage areas from a target region to identify gaps in transit access. Conservation managers subtract already-protected areas from priority habitat to focus acquisition efforts. Utility companies erase served areas from franchise territories to identify areas needing infrastructure expansion.

The difference operation is not commutative: subtracting A from B produces different results than subtracting B from A. Like other geometric operationsGeometric OperationsGeometric operations are spatial transformations applied to vector geometries, including union, intersection, differe..., precision issues at shared boundaries can create sliver polygons. For bidirectional analysis where exclusive areas from both inputs are needed, the symmetric difference operation is more appropriate.