Examples are topographic maps, road maps, weather maps. This normally involves a mathematical model that transforms the locations of features on the earth's surface to locations on a two-dimensional surface. Because the earth is three-dimensional, some method must be used to depict the map in two dimensions. Therefore such representations distort some parameter of the earth's surface, be it distance, area, shape, or direction. The coordinate units in which a geographic data set is stored.
Map units can be inches, centimeters, feet, meters, or decimal degrees.
This file may include at what scale the data was captured, what coordinate system it is in or where the file originated. The official reference ellipsoid used for the primary geodetic network in North America. The beginning and ending locations of a line on a digital map. A node is topologically linked to all lines that meet at the node. A relation in which one record in a table is related to many records in another table.