FOR SEVEN decades Tokyo was considered the world’s most populous city. That was 15 years too long, according to data released last month by the UN. Until recently the organisation’s statisticians accepted national governments’ definitions of where their cities began and ended; their latest report accepts the reality of urban sprawl. By their new measures, Jakarta (pictured), Indonesia’s capital, jumps to the top of the board with 42m people, about as many as Canada. Dhaka, capital of Bangladesh, with 37m, has also pulled ahead of Tokyo, with 33m. Delhi and Shanghai, with around 30m people each, fill out the top...