Half of world population live in cities

http://news.bbc.co.uk/2/hi/science/nature/4561183.stm

"In 1900, only 14% of humanity lived in cities. By the century's close, 47% of us did so. This change is revealed in the growth of the number of medium-sized cities. In 1950, there were 83 cities with populations exceeding one million; but by 2000, this had risen to 411. "

"While the world's urban population was just one billion in 1804, by 1985 it had risen to two billion and by 2002 it was three billion. If the trend continues, the world's urban population will double every 38 years, say researchers. "

"In the US, 80% of the population lives in cities."