Look, I made a thing! After I saw the awesome blog post on city street orientations, I generated some charts for European and German cities (and refactored Geoff's IPython notebook into a script on the way). If you want to see a map of your favourite city in this style, tell me about it and I'll see what I can do.
@siccegge @popefucker It's also got a lot to do with how much of the city was built in a planned matter (which doesn't necessarily correlate with age), how much of the city's size grew by annexing other villages (which have their own directions, usually), if there is a river and if that river is curved, etc. Also, compare to the original blog post for American cities, which are terribly griddy and aligned.