A polygon is a type of geometry containing an array of rings and a spatial reference. Each ring in a polygon contains an array of point coordinates, where the first and last point are the same. In most cases, a polygon is composed of a single ring of points, but it can also contain many rings representing independent areas or holes. To create a topologically correct polygon, exterior rings are oriented clockwise, and interior rings (holes) are oriented counter-clockwise. Point coordinates are expressed as x,y values. Each coordinate can also optionally include a 'z' value for height and / or an m value for measure (commonly used for linear referencing). When a ring in a polygon is selected, all rings are highlighted.