How do you make urban provinces with pictures?

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I decided that I didn't like the fact that Vienna, Paris and Rome aren't urban in the game: I thought they should be. So I decided to turn them into urban provinces, with appropriate little pictures. But I'm not sure how to do it. What files do I have to change, and what does the picture have to be like to work? Even more useful might be if someone has already done this so I can 'borrow'.

Thanks a lot!