There is a tremendous number of map and grid projections available to use and each will distort the surface of the earth in its own manner. The projection that a cartographer will use will depend on several things. Size and location are important considerations in choosing the correct projection when creating or selecting a map. Good qualities of a projection map are consistent area scale, good land and ocean shape, parallels that are parallel, and a consistent linear scale throughout the projection. Creating a map projection is actually a mathematical process.
Geometry plays a very important role in the creation of a map projetion.
The Mercator projection is one of the most recognizable and most widely used projections available today. The mercator projection is a conformal one in that the land masses are represented in their true shapes. This means that one every point on the projection angles are shown correctly. This also means that the farther away from the equator you get the more distortion is prevalent. The basis of the mercator projection is that of the globe projected onto a cylinder.