Map Projection Tutorial

Why are map projections an issue in GIS?

In many respects, GIS has freed us from the constraints of modelling the spatial relationships using a drawing on paper. For example: However, the spatial representation of data in GIS remains tied to a mapping plane. Map projections are the means of representing an ellipsoidal Earth on a mapping plane. Area calculations are done on the mapping plane, not on the ellipsoid

By definition, topological relationships are not affected by projection transformations. However, areas, shapes, angles and distances are affected.

Map projection characteristics

Different map projections retain or distort the following quantities. It is not possible for any one projection to retain more than one of them over a large area of the earth.

Common projections

Some of the common projections in use are: