Geometry classes support the concept of applying a GeometryComponentFilter filter to the Geometry. The filter is applied to every component of the Geometry which is itself a Geometry and which does not itself contain any components. (For instance, all the {link LinearRing}s in {link Polygon}s are visited, but in a {link MultiPolygon} the {link Polygon}s themselves are not visited.) Thus the only classes of Geometry which must be handled as arguments to {link #filter} are {link LineString}s, {link LinearRing}s and {link Point}s.

A GeometryComponentFilter filter can either record information about the Geometry or change the Geometry in some way. GeometryComponentFilter is an example of the Gang-of-Four Visitor pattern.