To portray a spherical surface such as the Earth's simply, one could use a globe; this requires only a scale transformation. Relative distances and directions are not distorted. However, globes or even pieces of a spherical surface are not convenient and expensive. Thus we normally need a transformation to systematically handle the distortion when portraying a sphere on a flat surface.

Projections are methods for transforming the Earth's spherelike surface onto a flat plane. In this systematic transformation locations in 3 dimensional space are made to correspond to a 2 dimensional representation.

The lines of latitude and longitude that appear on the map are called graticule. No graticule can be drawn without some kind of projection.