When you have a lot of room, why don't people just spread out over the countryside? Owning, or at least being surrounded by land, would seem to make sense in a civilization that relies on agriculture. Yet cities keep growing, as they have for thousands of years. The explanation of this seemingly dry subject is made intriguing by the fact that it's from Wendover Productions, which is always fascinating.
The simple answer is that people like to live near other people when it's possible, because there are a lot of benefits to living in groups, like jobs, services, and culture. The story of cities is really the story of agriculture, which is the story of civilization. The video goes into quite a bit more detail. -via Digg