in fact, the city assigned areas to be specifically used for graffiti, often in compliance with basic guidelines for content.

going a step beyond this, the city sponsored classes and courses for anyone interested in learning the art, and even declared the 27th of march rio's official graffiti day.  

many neighborhoods benefited form this, suddenly receiving beautiful depictions of events, landmarks, or people specifically important to their part of town.

humor is often incorporated in the paintings, and depending on the period of the creation of the art, satire is incorporated in the art - especially during election years.