“Tokyo is the undisputed champion of mega-cities. With a population of 37.8 million, it dwarves second-place Delhi. The Japanese capital has such a big lead in population that even though it’s expected to lose about half a million people over the next 16 years, it will still be the world’s biggest metropolis in 2030, according to a new report by the United Nations:”
Source: Almost all of the world’s biggest cities will be in Asia and Africa by 2030 – Quartz