2. Making surfaces

‘Making surfaces’ considers the shape of surfaces and discusses the work of some of the early topologists, Möbius, Klein, and Riemann. It introduces the torus shape and shows how its Euler number can be calculated along with that of a sphere. It discusses closed surfaces—ones without a boundary—and how they can be divided up into vertices, edges, and faces. It then introduces one-sided surfaces such as the Möbius strip and Klein bottle, which are examples of non-orientable surfaces. The Euler number goes a long way to separating out different surfaces, with the only missing ingredient in the classification the notion of orientability.