Cartography

After locating their area of interest using latitude and longitude, cartographers must determine how best to represent that particular portion of the Earth's surface in two dimensions. They must do this in such a way that minimal amounts of distortion affect the geographic information the map is designed to convey.

In order to understand the difficulty of such a task, imagine an orange with lines similar to parallels and meridians inked onto its surface. Now imagine removing the peel from the orange in one piece. If the peel of an orange is laid out flat on a tabletop, the peel will crack and break in various places. The cracks and breaks will distort the original shape of the orange, and the inked lines will no longer bear the same spatial relationship to each other as they did when the peel was on the orange. If the peel is arranged so that there are no cracks, breaks, or distortions in the relationships between the lines on its surface, the peel will assume the shape of a hollow sphere. There are only two choices: a spherical, distortion-free arrangement or a flat, distorted arrangement.

Cartographers have developed map projections to transform geographic information from a spherical surface onto a planar surface. A map projection is a method for representing a curved surface, such as the surface of Earth, on a flat surface, such as a piece of paper, so that each point on the curved surface corresponds to only one point on the flat surface.

There are many types of map projections. Some of them are based on geometry; others are based on mathematical formulas. None of them, however, can accurately represent all aspects of the earth's surface. Inevitably there will be some distortion in shape, distance, direction or area. Each type of map projection is intended to reduce the distortion of a particular spatial element. Some projections reduce directional distortion, while others try to present shapes or areas in as distortion-free a manner as possible. The cartographer must decide which of the many projections available will provide the most distortion-free presentation of the information to be mapped.