In Songdo, South Korea, on land reclaimed from the Yellow Sea, bikes and electric cars have the right of way; houses and offices have a single switch to turn off appliances and air conditioning; and all the water is recycled.

The "aerotropolis" - which some have called the future of urban planning - was designed as a centrally-located home for companies (and their employees) who do business with China and the rest of Asia. The city is linked by a bridge to Incheon International Airport. By air, Shanghai is an hour away and Tokyo an hour and a half.

The size of central Manchester or downtown Boston, and halfway between Seoul and the airport, Songdo International Business District already has 22,000 residents and only one third of it is built. By 2015, 1,000 new buildings will be standing and one of greenest cities on earth will be completed. About 40% is green space - there is a Central Park with desalinated sea water lakes - and the opera house, library, museum, many of the restaurants and American-style malls are no more than a 12.5-minute walk apart. Stan Gale, the developer who was tasked with building the sustainable metropolis to meet the needs of a growing world population, claims that the buildings will use 20% less water and 14% less electricity than traditional ones.

It is thought that China alone will need 500 Songdo-type cities by 2030 to house and employ an urban population of one billion, and Gale is in talks to build in several cities, like Chongquin, Wuxi and Dalian. In the next five years, China's central government plans to invest $230 billion and build 45 new airports, raising its current number from 175 airports to 220. And perhaps, each of them will have their own Songdo.

CORRECTION: An earlier version of this story stated that Sondu is along the Yellow River instead of the Yellow Sea. It has been corrected above.