Subculture that interests me

I would like to research the subculture surrounding graffiti.  I find this to be an interesting topic due, in large part, to the diversity of both the writers and the styles.  Graffiti is pervasive in virtually every corner of every part of the world, from scratched off paint in toilet stalls to 20-foot high letters on warehouse roofs.  It can consist of anything from a name to a political slogan to a novel, and with my research, I hope to answer the question of why people begin write graffiti and what effects, social or otherwise, it has on them.