I wouldn’t consider myself being expert. Generally spoken graph theory is a big topic in many disciplines, in programming its widely used. Many search algorithms are based on graph theory. If you use google you basically apply graphs. Part of the graph theory are route problems, steiner tree is one example. Another is the shortest path or traveling salesman. Often route problems are explained with street networks. So its natural using it for city planning. However a real application is found in programming.
If you don’t know about the basics you won’t understand it, that’s was the intention of my first post.
Edit: I saw the Python script. If you already know programming and how to write graphs, then just google for it. There are many implementations around.