I've started reading The Life and Death of Great American Cities by Jane Jacobs. What has impressed me so far is that Jacobs has a deep appreciation for emergent order. For example, consider her description of why certain kinds of city neighborhoods are so safe (p. 71):
On Hudson Street, the same as in the North End of Boston or in any other animated neighborhoods of great cities, we are not innately more competent at keeping the sidewalks safe than are the people who try to live off the hostile truce of Turf in a blind-eyed city. We are the lucky possessors of a city order that makes it relatively simple to keep the peace because there are plenty of eyes on the street. But there is nothing simple about that order itself, or the bewildering number of components that go into it. Most of those components are specialized in one way or another. They unite in their joint effect upon the sidewalk, which is not specialized in the least. That is its strength.
The word "animated" is important here: Jabos observes that safe streets are busy throughout the day and most of the night, they regularly attract different kinds of people for different purposes, and they bring those people out onto the sidewalks (she describes her book as written for "foot people"). Those who live on such a street take ownership for the street. Similar to Eric Raymond's observation regarding open-source software that "with enough eyeballs, all bugs are shallow", Jacobs focuses on the presence of people who actively look at what happens on the street -- in effect showing that "with enough eyeballs, all crime is shallow". But it's not enough to observe: one must also take action by intervening when the situation warrants it. The result is a fabric of trust among those who live and work and visit on the street.
Later (p. 199), Jacbos talks about the importance of having a mix of economic activities in a neighborhood:
We residents on the street and on its more purely residential tributaries could and would support a modicum of commerce by ourselves, but relatively little. We possess more convenience, liveliness, variety and choice than we "deserve" in our own right. The people who work in the neighborhood also possess, on account of us residents, more variety than they "deserve" in their own right. We support these things together by unconsciously cooperating economically. If the neighborhood were to lose the industries, it would be a disaster for us residents. Many enterprises, unable to exist on residential trade by itself, would disappear. Or if the industries were to lose us residents, enterprises unable to exist on the working people by themselves would disappear.
These urban phenomena are not created ex nihilo by city planning departments. Instead, they emerge organically through the social and economic interactions of residents, workers, and visitors in neighborhoods that are fortunately situated and well-laid-out.
Peter Saint-Andre > Journal