In 2009, the percentage of the planet's population living in urban areas crossed the 50% threshold…this year the population of the world's cities will grow by a further 65 million people, equal in size to the total population of France…
As recently as 1990 the United States had the highest number of one million plus inhabitant urban agglomerations globally with a total of 33….by the year 2020 China will lead the world with 121 followed by India with 58…
Remarkably, in 2009 China generated some 40.9% of GDP from just 16.6% of its population living in the 35 largest cities.
From an interesting Credit Suisse report, Opportunities in an urbanizing world (pdf).