The ESRI shape representation is the geometry representation used in shapefiles.  Shapefiles can be used to interchange data with many GIS systems, and have become a de-facto standard in the industry. This document defines the organization of the geometry object. Geometry objects can be 2D, 2D plus elevations, 2D plus measures, or 2D plus elevations and measures.  

The shape type is the first byte, and is defined as shown below. All other geometric properties follow based on the shape type:

Note: Shape types not specified above (2, 4, 6, etc.) are reserved for future use.

See also

Shape types in xy space