Punching holes in polygons with a symmetric difference operation

Why, oh why would we want to punch holes in polygons and create a donut? Well, this is done for several reasons, for example, you may want to remove a lake polygon from a forest polygon that it overlaps since it sits in the middle of the forest and is, therefore, included in your area calculations.

Another example is where we have a set of polygons representing a golf course's fairways and a second set of polygons representing the greens that overlap these fairways. Our task is to calculate the correct number of square meters of fairways. The greens will create our donuts in a fairway's polygons.

This is translated into spatial operation terminology and means that we need to perform a symmetric difference operation or, in ESRI terminology, an "erase" operation.

Getting ready

In this example, we will create two sets of visualizations to see our results. Our output will generate Well Known Text (WKT) that is displayed in your browser...