text:  Martha Cooper and Henry Chalfant were speaking to Matt Pintus. Now, as I mentioned, graffiti goes back to the Roman times, and ever since there's been a debate about whether it should be seen as vandalism or street art, or indeed as an important vehicle for political expression. We're joined now by Marianne Vosloo, an artist curator who works in the field of urban art. First of all, what's the difference between graffiti and what gets elevated to street art?