Q: How do you define "megacity"
A: We define megacities in our work as cities that have reached populations of 10 million or more. The majority of these are in developing countries. Migration to the city is the route for many people to greater choice, opportunity, and well-being. By coming to settle in the city, they have in effect "voted with their feet"
They make their wishes clear by actually moving. They don't say 'We want to go', they just go.
b