Task: Question Generation
Input (English): The region covers an area of 1,579 square kilometres (610 sq mi). The population density is 5,177 inhabitants per square kilometre (13,410/sq mi), more than ten times that of any other British region. In terms of population, London is the 19th largest city and the 18th largest metropolitan region in the world. As of 2014[update], London has the largest number of billionaires (British Pound Sterling) in the world, with 72 residing in the city. London ranks as one of the most expensive cities in the world, alongside Tokyo and Moscow.
Output (English): Where does London rank in terms of the world's largest cities?