Cartography

Although the geographical coordinate system is useful for large areas, it can be awkward to use for small areas. Many city maps use rectangular coordinate systems. After the map is complete, a grid is superimposed over it. The horizontal lines of the grid are assigned one set of numbers or letters, the vertical lines are assigned another set of numbers or letters. An index of place names is generated, which lists the horizontal and vertical coordinates for each place shown on the map. Used in conjunction with an index of place names, the rectangular coordinate system makes it simple for map readers to locate particular places. The Universal Transverse Mercator (UTM) system divides most of the earth's surface into zones, each of which has its own rectangular grid system. Most global positioning system (GPS) receivers can be set to show locations in UTM coordinates.