magine a globe made of glass. Overlay pieces of silver in the shape of the landmasses. Now imagine a light at the globe’s center, casting land-shaped shadows in all directions. The cartographer’s job, roughly and poetically, is to gather those shadows and transform them into a reasonable portrait of the planet. This first, crucial step in mapmaking is called the projection. Projections fall into three basic categories: planar, conic, and cylindrical.

Picking the right projection is crucial for achieving the map’s objective.