Projection

Map projections are used to represent locations on the earth's surface, on a 2 dimensional map. Mathematical formula are used to calculate the positions on the map.

It is inevitable that some distortion will take place when locations are transformed from a curved surface to a plane. This distortion may involve angles, area, directions, distances or shapes. All these properties cannot be kept undistorted in a single projection. Usually the distortion of one property will be minimised, while other properties become very distorted. Different projection systems are best suited to different end uses.

Terminology used to describe different projection systems:

Conformal (Orthomorphic) Projections: A projection is conformal if the angles in the original features are preserved. Over small areas shape is preserved (but not over large areas like Greenland!) A line drawn with constant orientation to north, will be straight. Areas are not preserved. Generally areas near the margins of the map will have a larger scale than those near the centre. Example: On a Mecator projection map a straight line has a constant bearing which is extremely useful for navigation purposes. However, the projection greatly exaggerates the size of land masses at high latitudes, that is near the poles. In this case Greenland appears larger than South America although it is only 1/8th of the size.

 

Equal Area (Equivalent) Projections The representations of areas is preserved. Angles are deformed so most shapes are distorted. Example: Robinson equal area projections  A map of the world which maintains equal areas greatly distorts shape. There is now considerable consensus that the Robinson projection, while not totally preserving area, provides an excellent compromise between area and shape.

Equidistant Projections In fact no single projection will preserve all distances. On an equidistant map only the distances from the centre are at the same scale.

Other Projections Other unusual projections are sometimes used. This projection uses an oblique equirectangular method of projection.