What are map projections?

Map Projections:

There are many different ways of transferring the curved surface of the earth onto flat maps, but they are all called map projections. Imagine that the earth's surface is transparent, and that there is a light shining from its core. As a flat surface approaches the earth, an image of earth's surface is projected onto the flat surface. The way the flat surface is held against the lighted earth determines the kind of projection made.