Timothy B Lee compares urban density to free trade:
[O]nline communication isn’t a good substitute for face-to-face interaction. We’re both happier and more productive when we’re interacting with other people in person. And so high-density development patterns have the same kind of productivity-enhancing benefits that free trade does. Tall buildings, walkable neighborhoods, and a good transit system reduce the average cost of face-to-face interaction in exactly the same way that steam ships and low tariffs reduced the average costs of shipping goods to the other side of the world. In both cases, the result is greater wealth, on a per-capita basis.
The Dish 