URBANIZATION : By 2008, for the first time in history, half of the world's population will live in urban areas. By 2030, 4.9 billion people, or 60 percent of the world population, will be urban.

WEALTH: In 2005, megacities accounted for 9 percent of the world's US $59.4 trillion gross domestic product. Five megacities—Los Angeles, Mexico City, New York City, Osaka-Kobe, and Tokyo—were among the world's 10 richest. Those five combined were more than twice as rich as the other 15. GDP will grow on average 4.9 percent per year across 22 megacities by 2020, when their combined GDP will reach $9.4 trillion. NOTE: ALL GDP USES THE PURCHASING POWER PARITY METHOD.