GeographicComposite is a subclass of GeographicObject. An object belonging to this class contains other geographic objects. A watershed may be defined as a spatial composite, containing subbasins. Because a spatial composite is also a geographic object, recursion is allowed. Each subbasin could be a spatial composite consisting of ecosystem zones. As with the previously reviewed classes, a user is expected to define meaningful subclasses of GeographicComposite where appropriate. Thus, a user may specify Watershed and Subbasin as subclasses of GeographicComposite, and EcosystemZone as a subclass of GeographicObject.