I'm a sucker for city maps so I voted for Nenlast. BUT, your La Rueda idea tempted me too...because it sounds like a pretty cool idea. How about you work on the city map first and refine your ideas for the sort of abstract representation you plan for the other? There are a lot of good resources on visualization out there (just saw some new ones at Barnes & Noble the other night) but maybe look up Edward Tufte and follow that rabbithole for a while. It's inspirational if nothing else.