map projection

Three widely used map projections. If a light were placed at the centre of a transparent Earth, the shapes of the countries would be thrown as shadows on a sheet of paper. If the paper is flat, the azimuthal projection results; if it is wrapped around a cylinder or in the form of a cone, the cylindrical or conic projections result.

Way of showing the Earth's spherical surface on a flat surface. The most common approach has been to redraw the Earth's surface within a rectangular boundary. The main weakness of this is that countries in high latitudes are shown disproportionately large. The most famous such projection is the Mercator projection, which dates from 1569. Although it gives an exaggerated view of the size of northern continents, it is the best map for navigation because a line of constant bearing appears as a straight line.

In 1973 German historian Arno Peters devised the Peters projection in which the countries of the world retain their relative areas. In other projections, lines of longitude and latitude appear distorted, or the Earth's surface is shown as a series of segments joined along the Equator. In 1992 the US physicist Mitchell Feigenbaum devised the optimal conformal projection, using a computer program designed to take data about the boundary of a given area and calculate the projection that produces the minimum of inaccuracies.

The theory behind traditional map projection is that, if a light were placed at the centre of a transparent globe of the Earth, the surface features could be thrown as shadows on a piece of paper close to the surface. This paper may be flat and placed on a pole (azimuthal or zenithal), or may be rolled around the Equator (cylindrical), or may be in the form of a tall cone resting on the Equator (conical). The resulting maps differ from one another, distorting either area or direction, and each is suitable for a particular purpose. For example, projections distorting area the least are used for distribution maps, and those with least distortion of direction are used for navigation charts.