to generate exuberant diversity in a city's streets and districts, four conditions are indispensable:
- The district, and indeed as many of its internal parts as possible, must serve more than one primary function; preferably more than two. These must insure the presence of people who go outdoors on different schedules and are in the place for different purposes, but who are able to use many facilities in common.
- Most blocks must be short; that is, streets and opportunities to turn corners must be frequent.
- The district must mingle buildings that vary in age and condition, including a good proportion of old ones so that they vary in the economic yield they must produce. This mingling must be fairly close-grained.
- There must be a sufficiently dense concentration of people, for whatever purposes they may be there. This includes dense concentration in the case of people who are there because of residence.
-- Jane Jacobs, The Death and Life of Great American Cities, which I'm reading all the way through right now and which is transforming my view of everything.