Also inspiring, and possibly useful for the "world turned upside-down" project, look up Shepart Fairey, and American street artist. His work started as plain old stickers posted around towns (the useful bit, to be honest, seeing as we're looking for ideas regarding artwork incorporating towns), and later became a well-known campaign poster (see left) used to promote Obama during the most recent presidential elections in the US.
For his bio:
http://www.thegiant.org/wiki/index.php/Shepard_Fairey
For his artwork:
http://obeygiant.com/
http://www.shepardfaireyprints.com/
