Metropolitan Area: 23.9 million people

Population: 10.3 million

Seoul has grown rapidly since the war between the two Koreas (1950-1953). Today, almost half of the population lives in Seoul and its suburbs. In recent years, Seoul has modernized the transport system of the city and created a lot of public green spaces.

9) Mumbai, India

Metropolitan area: 21 million people

City: 13 million people

Mumbai -also known as Bombay until the name was officially changed in 1995- is the most populous city in the world. With high birth rates and the constant influx of immigrants, it is expected that the population of this city will experience a tremendous growth over the next ten years.