The things that occupy the geographic world, described and measured in various ways as points, lines, areas, or volumes. 'In practice, points, lines, and areas are most often represented in the following standard forms: Points as pairs of coordinates, in latitude/longitude or some other standard system; Lines as ordered sequences of points connected by straight lines; Areas as ordered rings of points, also connected by straight lines to form polygons. In some cases areas may contain holes, and may include separate islands, such as in representing the State of Michigan with its separate Upper Peninsula, or the State of Georgia with its offshore islands. This use of polygons to represent areas is so pervasive that many spatial analysts refer to all areas as polygons, whether or not their edges are actually straight.' For more information, see
http://www.spatialanalysisonline.com/output/
