But China's population statistics can be particularly misleading.

"Virtually overnight, Chongqing has become the largest city not only in China, but in the world," Time Magazine proclaimed in 2005.

But it wasn't true - Chongqing is not the largest city in the world, or even in China.

Why do so many people think it is?

Professor Kam Wing Chan of the University of Washington in the United States, who has made a career out of correcting people's exaggerated claims about Chinese population statistics, explains that what China calls a municipality or city is better understood as a province.

Many of the 30 million people who are said to live in the city of Chongqing are actually agricultural workers living in a rural setting, he says.

In fact, he says, the area is so huge it's about the size of Austria.

"And if you were to travel from the downtown area to some of the peripheral areas where those 30 million live, it might take a day or two because the road conditions are not that good. So, this cannot be possibly called a city. Because when we call a place a city the general understanding is that we're talking about a commuting zone."

Professor Chan calculates that a more reasonable estimate of the urban population of Chongqing is six or seven million.