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

IK's World Trip/Flickr

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.

China has long had a large population. In 1897 the country contained 363 million people — still 45 million more than the current population of the US.

It wasn't until a century later, however, that the rural Pearl River Delta began to take shape as an urban hub during the tech and manufacturing booms of the 1990s.

By the early 2000s, the changes were plainly visible. Take the NASA satellite photography over a period of 30 years. Here's 1973. The wispy gray regions are the infrastructure projects quickly popping up around the region.