2 dimensional (graphical) topological representation of a sphere One page 37 of this pdf - Surfaces - it gives a graphical representation of a sphere in 2 dimensional topological format. I don't see how the image for a sphere here actually describes a sphere. Does anyone know how this image describes a sphere?

It might be easier to think about it the other way round. Imagine you have a sphere and you cut from the north pole down to the south pole and then pull it apart and try to lay it flat. If the material was suitably stretchy then it would be able to lay flat on a table and would be (topologically) a disk because there are no 'holes'.
Now, run this in reverse. Start with a disk, bend it a bit and then 'zip up' the boundary to get a sphere.
