The great story of the tube map is that Harry (Henry) Beck working as an electrical draughtsman based the design of the tube map on an electric circuit diagram.
Dig a little deeper into the history though, and this ‘fact’ is debunked, but something that certainly did happen is that Beck had a little fun by reversing this around, and drawing a Tube Map in an electrical-diagram style.
We stumbled across this yesterday on the marvellous Map : Graphical Approach website, which has got lots of hi-resolution diagrams of the tube map which are worth clicking on and having a look at, including this wiring-diagram one …
Electrical Tube Map