What are map projections?
A map projection simply is a representation of the round, 3D
surface of the earth onto a flat, 2D map. There are different map
projections such as Mercator and Robinson each of which have
advantages and disadvantages.
The appropriate projection for a map depends on the scale of the map and the purposes for which it will be used. For example, a Mercator projection has straight rhumb lines and is therefore excellent for navigation, because compass courses are easy to determine, but there is distortion near the poles.