China is home to one-fifth of the world’s population, as well as one of the starkest divides between the rural and urban. As evidenced by this map, when split roughly in half, 94% of people live in the more urbane cities in the east, while a much smaller percentage of people (6%) lives in the west. Such high numbers in cities can go a long way in explaining the issues the country faces when it comes to pollution.
Source: all-that-is-interesting.com