In many parts of the inner city, graffiti sprouts as naturally as weeds, or flowers, depending on your perspective. The San Francisco Arts Commission (SFAC) has been trying to reach the (mainly) youth population that's behind tagging in a variety of ways over recent years, and last week it unveiled one of its most intriguing initiatives yet.

GraffCity is an app that turns your iPhone into virtual spray can. You can point it at any building or vehicle or sidewalk (or even the sky) and tag without breaking the law or defacing someone else's property.

"It's quite amazing, actually," says Tyra Fennell, Arts Education Program Manager for the SFAC. "The tag looks like it's right there on the building."

But it's only there virtually. Once you upload your work to Facebook or to the website associated with the app, the augmented reality mode embedded in the app uses GPS to allow you to see other people's virtual tags as well.

Developed by global advertising giant McCann Erikson as a pro-bono project, GraffCity does something else – it creates a potential global market for graffiti artists to exhibit their work.

"Taggers want notoriety," says Fennell. "Now they will have a global capability to reach people. Graffiti is huge overseas."

Of course, a certain proportion of taggers do not consider themselves artists at all and have other intentions when they spray-paint buildings in their neighborhoods.

"Those who are vandals, who want to mark territory and so on, we will probably never reach," says Fennell. "But we hope to alleviate some of the problem through efforts like GraffCity. We also send established muralists into the schools to teach kids the difference between public and private property and to learn the concept of permission."

The arts commission has been trying various experiments using technology, including social media, to engage with youth who might otherwise become vandals. Last year's SFJam, for example, was a big success.

With GraffCity, Fennell says, "We hope to offer this app to kids who are idle and might use it to express themselves. We tell them, 'here's a way to legitimize yourself as an artist.'"