It's an amalgam of engineering, architectural, and human qualities that he muses on here in the WSJ's weekend edition. Size is obviously important:
A city can't be too small. Size guarantees anonymity"”if you make an embarrassing mistake in a large city, and it's not on the cover of the Post, you can probably try again.
Density is a must:
If a city doesn't have sufficient density, as in L.A., then strange things happen. It's human nature for us to look at one another"” we're social animals after all. But when the urban situation causes the distance between us to increase and our interactions to be less frequent we have to use novel means to attract attention: big hair, skimpy clothes and plastic surgery.
Why can't urban planners write like this?! Here's Bryne's dead-on observation that counters the nostalgia that too often infects most urbanites:
The perfect city isn't static. It's evolving and ever changing, and its laws and structure allow that to happen. Neighborhoods change, clubs close and others open, yuppies move in and move out"”as long as there is a mix of some sort, then business districts and neighborhoods stay healthy even if they're not what they once were. My perfect city isn't fixed, it doesn't actually exist, and I like it that way.