There is a widespread belief that americans hate cities. I think it is probable that Americans hate city failure, but, from the evidence, we certainly do not hate successful and vital city areas. On the contrary, so many people want to make use of such places, so many people want to work in them or live in them or visit in them, that municipal self-destruction ensues. In killing successful diversity combinations with money, we are employing perhaps our nearest equivalent to killing with kindness.
But ideal cities are very much the product of their own ages. Designed as complete urban statements, they bear the unmistakable imprint of their own culture and world view in every street and building. And yet to be successful a city has to be open to continuous development, free to evolve and grow with the demands of new times. Like science fiction accounts of the future, ideal cities quickly become outmoded.
To generate exuberant diversity in a city's streets and districts four conditions are indispensable:1. The district, and indeed as many of its internal parts as possible, must serve more than one primary function; preferably more than two...2. Most blocks must be short; that is, streets and opportunities to turn corners must be frequent.3. 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.4. There must be a sufficiently dense concentration of people, for whatever purposes they may be there...
I have been dwelling upon downtowns. This is not because mixtures of primary uses are unneeded elsewhere in cities. On the contrary they are needed, and the success of mixtures downtown (on in the most intensive portions of cities, whatever they are called) is related to the mixture possible in other part of cities.
You can neither lie to a neighbourhood park, nor reason with it. 'Artist's conceptions' and persuasive renderings can put pictures of life into proposed neighbourhood parks or park malls, and verbal rationalizations can conjure up users who ought to appreciate them, but in real life only diverse surroundings have the practical power of inducing a natural, continuing flow of life and use.