A city plays the role of a great big magnet that's sucking people up.

One of the remarkable things about slums is that they do develop their own social organization and economy and even culture that is, on some level, functional and in some cases, remarkably resilient. This is kind of amazing.

Slums could be thought of as the development of a special organ, or they could be thought of as a tumor that's grown, and in some ways is unhealthy and could ultimately lead to the city's destruction. My own feeling is that slums are probably a bit of both.

My provocative statement is that we desperately need a serious, scientific theory of cities and scientific theory means quantifiable, relying on underlying generic principles that can be made in a - put into a predictive framework. That's the quest.

Tell me the size of a mammal and I can tell you, to about 85 per cent level, pretty much everything about its physiology and life history, such as how long it is going to live, how many offspring it will have, the length of its aorta, how long it will take to mature, what is the pulse rate in the ninth branch of its circuitry.