Mapping a round Earth

Mapping the whole Earth is harder, because our planet is not flat. It is nearly a sphere, a ball.

Why 'nearly'? Because it is not a perfect ball: it is slightly flattened at the poles. But in practice we treat it as a sphere. Notice that the book tells you honestly where it is making things simpler.

Here is a big claim: a sphere cannot be shown accurately on a flat sheet of paper. Not just 'difficult': not possible. You can prove it yourself. Peel an orange so that you get three or four large pieces of skin, then try to press them flat on a table. You cannot do it without tearing them at the edges.

A curved surface will not lie flat, and the Earth's surface is curved. So every flat map of the world is stretched somewhere. That is not the mapmaker's mistake; it cannot be avoided.

Now think of a globe: a sphere with a map drawn on it. It may be a map of the Earth, the Moon, the planet Mars, or even the stars and constellations in the sky. A globe is usually made of metal, plastic or cardboard.

Because the globe and the Earth have the same round shape, a globe shows the Earth's geography better than a flat map. You cannot fold a globe into your pocket, but it never gets the shape wrong.