Graffiti and Public Art .. is it vandalism?

Graffiti and public art has become a major part of urbanised communities, creating colourful and flamboyant streets. However, there’s still the debate over whether this public art is in fact art, or is it vandalism? People’s personal graffiti tags on walls of abandoned buildings is usually the image we picture when talking about graffiti. But what about the public street murals artists dedicate their time and creativity to? It is said that graffiti art can be used to decrease vandalism.. is this true?