January 15, 2013, 10am PST
When the Kumbh Mela, a 48-day Hindu festival held every four years, starts this week in northern India it will be the largest gathering in history. Researchers are using the opportunity to study the formation and inner-workings of a pop-up mega city.
January 27, 2011, 10am PST
China plans to create the world's largest mega-city, which will be geographically 26 times larger than Greater London and double that of Wales.