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MySQL 9.4 Reference Manual  / ...  / Data Types  / Spatial Data Types  / The OpenGIS Geometry Model  /  The Geometry Class Hierarchy

13.4.2.1 The Geometry Class Hierarchy

The geometry classes define a hierarchy as follows:

  • Geometry (noninstantiable)

    • Point (instantiable)

    • Curve (noninstantiable)

      • LineString (instantiable)

        • Line

        • 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 ofGeometry 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).

The baseGeometry class has subclasses forPoint,Curve,Surface, andGeometryCollection:

  • Point represents zero-dimensional objects.

  • Curve represents one-dimensional objects, and has subclassLineString, with sub-subclassesLine andLinearRing.

  • Surface is designed for two-dimensional objects and has subclassPolygon.

  • GeometryCollection has specialized zero-, one-, and two-dimensional collection classes namedMultiPoint,MultiLineString, andMultiPolygon for modeling geometries corresponding to collections ofPoints,LineStrings, andPolygons, respectively.MultiCurve andMultiSurface are introduced as abstract superclasses that generalize the collection interfaces to handleCurves andSurfaces.

Geometry,Curve,Surface,MultiCurve, andMultiSurface 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, andMultiPolygon are instantiable classes.