The OpenGIS Geometry Model • LinearRing • Surface  (noninstantiable) • Polygon  (instantiable) • GeometryCollection  (instantiable) • MultiPoint  (instantiable) • MultiCurve  (noninstantiable) • MultiLineString  (instantiable) • MultiSurface  (noninstantiable) • MultiPolygon  (instantiable) It is not possible to create objects in noninstantiable classes. It is possible to create objects in instantiable classes. All classes have properties, and instantiable classes may also have assertions (rules that define valid class instances). Geometry  is the base class. It is an abstract class. The instantiable subclasses of  Geometry  are restricted to zero-, one-, and two-dimensional geometric objects that exist in two-dimensional coordinate space. All instantiable geometry classes are defined so that valid instances of a geometry class are topologically closed (that is, all defined geometries include their boundary). Geometry ,  Curve ,  Surface ,  MultiCurve , and  MultiSurface  are defined as noninstantiable classes. They define a common set of methods for their subclasses and are included for extensibility. Point ,  LineString ,  Polygon ,  GeometryCollection ,  MultiPoint ,  MultiLineString , and MultiPolygon  are instantiable classes. Geometry  is the root class of the hierarchy. It is a noninstantiable class but has a number of properties, described in the following list, that are common to all geometry values created from any of the  Geometry subclasses. Particular subclasses have their own specific properties, described later. A geometry value has the following properties: 2052 Geometry Properties 11.4.2.2 Geometry Class • Point  represents zero-dimensional objects. The base  Geometry  class has subclasses for  Point ,  Curve ,  Surface , and  GeometryCollection : • Curve  represents one-dimensional objects, and has subclass  LineString , with sub-subclasses  Line and  LinearRing . • Surface  is designed for two-dimensional objects and has subclass  Polygon . • GeometryCollection  has specialized zero-, one-, and two-dimensional collection classes named MultiPoint ,  MultiLineString , and  MultiPolygon  for modeling geometries corresponding to collections of  Points ,  LineStrings , and  Polygons , respectively.  MultiCurve  and  MultiSurface are introduced as abstract superclasses that generalize the collection interfaces to handle  Curves  and Surfaces .