Editing Map projection (section)

===Choosing a projection surface===
[[File:Usgs map miller cylindrical.PNG|thumb|300px|A [[Miller cylindrical projection]] maps the globe onto a cylinder.]]
A surface that can be unfolded or unrolled into a plane or sheet without stretching, tearing or shrinking is called a ''[[developable surface]]''. The [[cylinder (geometry)|cylinder]], [[cone (geometry)|cone]] and the plane are all developable surfaces. The sphere and ellipsoid do not have developable surfaces, so any projection of them onto a plane will have to distort the image. (To compare, one cannot flatten an orange peel without tearing and warping it.)

One way of describing a projection is first to project from the Earth's surface to a developable surface such as a cylinder or cone, and then to unroll the surface into a plane. While the first step inevitably distorts some properties of the globe, the developable surface can then be unfolded without further distortion.