03/09/2012 07:12 am ET Updated May 09, 2012

The 9 Best Cities For Street Art Spotting (PHOTOS)

Street art, once thought of as synonymous with vandalism and disregarded, is now an art force to be reckoned with. As the art form has grown in stature, it's also grown up in terms of medium -- street art isn't about "tagging" walls with spray paint these days, as artists branch out into wheatpaste and woodblocks, showcasing their work inside art galleries nearly as often as on walls. Some street artists are household names, with their work commanding thousands of dollars and collected by individuals and museums. Street art has always been cool, but in the twenty-first century it's become an art.

Sometimes massive murals cover entire buildings and artists use their medium to create beauty in an otherwise gritty landscape as well as to express emotions of protest. Their tools include paint, tiles, laser light displays, yarn, stickers, and found objects, and in some cases simply selectively cleaning a dirty area creates an image in what's called "reverse graffiti."

Although street art is just as often found indoors as out nowadays, the best places to see street art in all its glory remains exterior walls, walls that artists usually don't have permission to use as a canvas. The cities highlighted below are each excellent places to find some of the world's best street art, but that doesn't mean there aren't other cities with great street art out there - all you need to do is look for it.

Here are 9 of the world's best cities for seeing street art.

Read more about art around the world: Photos by: Garrett Ziegler, astuecker, unusualimage, Richard Munckton, Melanie-m, Lord Jim, isaac"licious, frerieke, hragv