Here Are The World's 21 Mega-Regions

Cities are the future of the world, especially in urban markets. Over half the world's population now lives in cities, and by the middle of the century, more than 7 in 10 people will live in cities, according to the UN. Almost all of this urban growth will take place in emerging economies.

This map, from Citi Research, shows the location and size of major cities around the world, and the share of population in each country living in cities, based on UN data:

Asia, especially China and India, has a huge number of cities, but their populations still remain spread out, compared to the more urbanized Western Hemisphere and Europe.

The largest mega cities, those with over ten million residents, are shown in the map as red circles. Below is a list of those largest cities, with their approximate 2010 populations, from the UN's 2012/2013 "State of the World's Cities" report: