Safety and security are two of the biggest challenges faced by each and every metropolis. Whether earthquake, terrorism, flood or just crime, it\'s the geology, politics and social makeup of the megacities that make them some of the most profitable and dangerous places to live.

Andrew Marr looks at how people live in London, Dhaka, Tokyo, Mexico City and Shanghai.

Andrew finds out how megacities stay fed, and joins Mexico City\'s traffic cops in the air.