China is building the world's largest city - and it already has more people than South Korea

For the past decade, China has been on a mission to build the world's biggest city by combining a number of large cities into one giant megacity.

With a current population of roughly 57 million housed inside a 15,000-square-mile perimeter, the Pearl River Delta is a region roughly the size of West Virginia but with 30 times more people.

It's made up of the cities of Shenzhen, Dongguan, Huizhou, Zhuhai, Zhongshan, Jiangmen, Guangzhou, Foshan, and Zhaoqing.

Each city's population ranges from nearly 2 million to more than 14 million, which, by 2030, China hopes to unite into an all-powerful megacity with an economic output around $2 trillion.

Whether that's feasible is still a mystery, but it's one the country is set on solving.