# Empty, simple or closed geometries

A geometry is empty if it does not have any points. Curves and multicurves may be closed. The values of some geometry subtypes (linestrings, multipoints, and multilinestrings) are either simple or non-simple.

- Empty geometries
- The envelope, boundary, interior, and exterior of an empty geometry are
not defined and will be represented as null.
An empty geometry is always simple. Empty polygons and multipolygons have an area of 0.

- Simple geometries
- A geometry is simple if it obeys all the topological rules imposed
on its subtype and non-simple if it doesn't.
A linestring is simple if it does not intersect its interior. A multipoint is simple if none of its elements occupy the same coordinate space. Points, surfaces, multisurfaces, and empty geometries are always simple.

- Closed geometries
- A curve is closed if its start and end points are the same. A multicurve is closed if all of its elements are closed. A ring is a simple, closed curve.