While it is easy to draw the system of meridians and parallels on a globe, it is not possible to draw this system on a flat piece of paper (a map) without introducing some distortion. A wide variety of methods have been developed to reduce this distortion during the construction on a map. This process of constructing a map, the transferring of the meridians and parallels to a flat sheet of paper, is a geometric exercise called projection, and the resulting product is called a map projection. The map projection selected for use by the cartographer, one who draws maps, depends on the purpose of the map and the material to be presented.

     The variety of map projections available include a group of projections that preserve the property of area, equal-area projections. On an equal-area, a coin placed any place on the map will cover the same area. These projections distort shape and the angular relations between meridians and parallels.

     Conformable maps represent a group of projections that preserve shape but greatly distort area. Because many publications prefer to present maps that preserve shape, readers often have a mistaken impression of the relative size of the continents. An example of this is the size of Greenland, actually about the same size as Mexico, but on a conformable map of the world it appears many times larger. There are a variety of projections that preserve angular relationships between the meridians and parallels or that, while preserving none of these properties, are compromises used for specific purposes. Most of the U.S.G.S. maps are drawn on a polyconic projection. This projection preserves neither shape nor area, but for the small area represented the distortion of both is at a minimum.