Source: [[Reference Notes/Scale]] 200 years ago, the US was predominantly agricultural, with about 4 percent of the population living in cities. Today, that figure is 80 percent. Today, no country comes close to being just 4 percent urban. The closest, Burundi, is about 10 percent urbanized. In 2006, the planet crossed a threshold in which more than half of the world's population now lived in cities. A hundred years ago, it was 15 percent, and in 1950 it was 30 percent. It is expected to rise to 75 percent by 2050. When averaged out, this means that a million and a half people will be be urbanized each week. Every few months, a city the size of metropolitan New York, about 15 million people, will be added. China will be adding 300 new cities of over a million people in the next 20 to 25 years, which is the equivalent of the entire population of the US. In 1950, China was about 10 percent urbanized. Adding India and Africa, we have the largest migration of human beings in history.