Which one you regard as the holder of the title, all depends on what you mean by city. Most experts will tell you that Tokyo is the world's largest metropolis, with a population of about 36 million people.But the core of the city has only eight million people living in it.he 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.