"The magic of squatter cities is that they are improved steadily and gradually by their residents. To a planner's eye, these cities look chaotic. I trained as a biologist and to my eye, they look organic. Squatter cities are also unexpectedly green. They have maximum density-1m people per square mile in some areas of Mumbai-and have minimum energy and material use. People get around by foot, bicycle, rickshaw, or the universal shared taxi.
Not everything is efficient in the slums, though. In the Brazilian favelas where electricity is stolen and therefore free, people leave their lights on all day. But in most slums recycling is literally a way of life. The Dharavi slum in Mumbai has 400 recycling units and 30,000 ragpickers. Six thousand tons of rubbish are sorted every day. In 2007, the Economist reported that in Vietnam and Mozambique, 'Waves of gleaners sift the sweepings of Hanoi's streets, just as Mozambiquan children pick over the rubbish of Maputo's main tip. Every city in Asia and Latin America has an industry based on gathering up old cardboard boxes.' There's even a book on the subject: The World's Scavengers (2007) by Martin Medina. Lagos, Nigeria, widely considered the world's most chaotic city, has an environment day on the last Saturday of every month. From 7am to 10am nobody drives, and the city tidies itself up."
Brand suggests that this sort of dense urbanization organically encourages a more efficient use of land and resources.