Political?

The Berlin Wall. The Berlin Wall was a product of political drama giving birth to what has been described as the largest canvas in the world. External Link Concerning the Berlin Wall

Artistic?
Keith Herring. He saw art in what other had seen as defiling public property. One of his great influences was the Berlin Wall as well as Graffiti he saw on trains and walls.

Criminal?
Crews Groups of graffiti artists "bombing" public property from alley street walls to underground trains. Is this crime or expression of art?

Cultural?
Hiphop Culture: Rap, hiphop, breakdancing, MCs meshes with graffiti

.