2012-03-13
The Sizes of Cities
What’s the largest city in the world? This seemingly simple question is actually rather complicated to answer. In my post Concentric Londons, I noted how you can define the city in various ways (and I still missed a few), while my complaints about the interesting but flawed visualisation showing “how much room would you need for the world’s population if the city were as dense as…” noted that the cities picked were defined very differently.
It turns out that the BBC’s excellent More or Less tackled the issue in a special edition, which (thankfully) is also available as a BBC News Magazine article (for those of us who prefer reading words to hearing them). After noting some of the problems I’ve covered - is a city the same as the government region defining it, or is it a contiguous urban area, or perhaps a zone of influence? - they settle on Tokyo/Yokohama, at 30 million plus, as the most reasonable answer to the question.
Curiously, it turns out that there is no official UN (or other reliable worldwide) definition of a city. Where Paris excludes its periphery, London extends nearly to the M25; where New York excludes Jersey City, Greater London expanded in the 1960s to swallow chunks of Essex. That’s not even to consider cities such as Cairo, Nairobi, or Rio de Janeiro, where informal building means a density and sprawl that’s a laissez-faire economist’s dream.
However, that wasn’t the end of the show. The final section covered China’s cities, which, if you believe the numbers, are growing like nothing on earth. However, the numbers may not be that trustworthy. Official statistics, as noted by guest Professor Kam Wing Chan, conflate cities with provinces, which can be largely rural, inflating estimates by as much as a factor of five:
The largest city in China is actually Shanghai. It is commonly thought to have a population of 20 million, but Professor Chan thinks 16 million is a better estimate.
He says everyone just loves to think China’s cities are bigger than they actually are. He has even had to correct fellow experts at a world conference on global megacities of the future.
One thing’s for certain: you can’t take the numbers at face value.
