wow that looks like a great map, it also answered some questions i havent asked yet about if maps could "progress" as you have done.
i was thinking about some map ideas based on london locations and things like tower bridge would be beatiful maps but tend to be quite linear, however with a progression system like you have they could work very well.
i might go photographing around parts of london (a risky business these days that can get you harassed by the police

) to get some possible map locations documented for people who are looking to create but need a basis to work from.