Graph Tutorial

The graph module is responsible for the bulk of questions this month; one thing that makes answering these questions hard is the lack of a test case or example program that could be used as a reference point.

With that in mind I would like to put together a simple "Graph" tutorial; please use the comments to outline the ideas of what you would like to see ... however a couple of guidelines:

1. We need a sample dataset - a public sample data set. I will consider the Tiger Roads dataset as a good reference point unless someone can think of something smaller (and more international). Is there a good way to extract just a bit of open street maps?
2. We step by step instructions need to be simple and straight forward and very well tested!
3. The tutorial has to be visual in some fashion
4. We can save many of the other goals of the graph module for the bonus questions (such as the differences between the path finding algorithms).
5. We follow a "code first" writing style; so no explaining things in the middle of the step by step instructions
6. We can put and explaining after the code; but we should save any detailed background on graph theory for the peanut gallery (or wikipedia). We want results in a tutorial - not theory.