Mumbai - according to the UN - has a population of 19 million. And the UN forecasts that total will rise to more than 26 million by 2025. At that point, it would be the most heavily populated "urban agglomeration" in the world, apart from Tokyo and its surroundings. Mumbai's increase in population will partly be caused by increasing life expectancy and partly by migration from other, poorer, parts of India. Although Mumbai is India's commercial capital and rents for luxury apartments are some of the highest in the world, it is estimated that more than half the city's population live in slums. And controversial plans to redevelop the slums highlight some of the problems faced by mega-cities around the world.
