In Dhaka, the capital of Bangladesh, the number of squatters has incresed from 275,000 to 3.4 million over the past 30 years. Their communities occupy only 5.1 percent of the city's total land but are home to 37.4 percent of the city's population. And, while the total population density in the city is 121 people per acre, you have to multiply that by 7 in the shantytowns, which boast 891 persons per acre.
Amazingly (and contrary to the myth that there's an absolutely bleak future for squatters) more than half of these people have been able to knock down their mud and cardboard dwellings and rebuild them from brick.
You can read more on a recent census of the Dhaka's shanties (funded in part by the United States Agency for International Development!!!) in The Daily Star.