7 Billion Humans in 2011 | National Geographic Magazine: Extreme Mustang Makeover | Fort Worth, Texas, USA

Extreme Mustang Makeover | Fort Worth, Texas, USA

Extreme Mustang Makeover | Fort Worth, Texas, USA

The urban population of developing countries is expected to grow by a million people every five days through at least 2030, while the rural population falls. Many cities will eat into prime agricultural land unless they grow in density, not extent. And nearly half of urban population growth by 2015 will occur in cities of fewer than half a million people.

—Joel E. Cohen, author of “How Many People Can the Earth Support?”

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