An article by Jamais Cascio at Worldchanging
"Some numbers: today, there are approximately one billion squatters -- about 1 in 6 people on the planet; by 2030, it's estimated there will be two billion squatters, or about 1 in 4; by 2050, there could be three billion squatters, or 1 in 3. Some 200,000 people move from rural communities to urban communities every day, globally. That's around 70 million per year, or 130 every minute. Inevitably, the cities of the future will be built by squatters."