Megacities.

Forbes published an article on megacities, huge urban clusters.
Here is a summary (population i guess refers to the urban area surrounding the city):

#1. Tokyo, Japan
Projected Population in 2015: 35.5 million
Population in 2005: 35.2 million

#2. Mumbai, India
Projected Population in 2015: 21.9 million
Population in 2005: 18.2 million

#3. Mexico City, Mexico
Projected Population in 2015: 21.6 million
Population in 2005: 19.4 million

Tokyo densities

1. Donki- department store
2. Commes des Garcons shop
3. Meiji Temple
4. Hachiko square in Shibuya

A quick glance on Tokyo different densities which remind us once more not to give a single opinion on japan. Differences coexist side by side.