Tonight I saw a film called Bomb It, a documentary about international graffiti art.
It started out with Philadelphia and New York, but the most interesting parts were about graffiti artists around the world. Some people do street art primarily because it's dangerous and illegal, but a lot of people do it because they have something to express, and they want/need to do it in a public way. It's a very social, political, and personal art form. So, in different countries you find that people are driven to make different social and political statements. Plus the cultural attitude towards public spaces and street art varies, and that also contributes to different dynamics around the globe.
My only complaint about the film is that some really interesting topics were touched on so briefly - I wish I could have seen more. Apparently they had many hundreds of hours of footage, but of course in editing it down to a feature length doc, there's only so much they can include. I think this would actually work really well as a series, so I hope they get to do more with it!