Analysis of Universal Transverse Mercator projection and Coordinate System
The familiar Mercator projection used on so many world maps is a cylindrical projection, meaning the globe is encircled by an imaginary cylinder touching at the equator, and the earth is projected onto the cylinder. Contrary to a lot of geography texts, the projection is not what would result from placing a light at the center of the earth and projecting the surface onto the cylinder. (That projection called the cylindrical gnomonic, results in extreme distortion in polar areas and has virtually no practical uses. The term "map projection" actually means any mathematical transformation of the globe onto some other surface, including many that can't be physically realized by any actual optical projection system. The Mercator projection is a conformal projection, meaning that angles and small shapes on the globe project as the same angles or shapes on the map. The price paid by all conformal projections is great variation in scale away from the central portions of the map. Greenland on a Mercator map looks as big as South America, though it has actually only 1/8 the area. However, a small portion of the Greenland coast (or any small region, in fact) has the same shape on the map as it does on the ground. Because the Transverse Mercator projection is very accurate in narrow zones, it has become the basis for a global coordinate system called the Universal Transverse Mercator System or UTM System. The globe is subdivided into narrow longitude zones, which are projected onto a Transverse Mercator projection. A grid is constructed on the projection, and used to locate points. The upside of the grid system is that, since the grid is rectangular and decimal, it is far easier to use than latitude and longitude. The downside is that, unlike latitude and longitude, there is no way to determine grid locations independently. The scale along the central meridian of each zone is 0.9996 of true scale. True scale occurs about 180 kilometers east and west of the central meridian.