Cities are not planned — they accumulate. The great urban theorist Jane Jacobs, writing in the 1960s, made this observation against the grain of her times, when planners across the Western world were demolishing old neighbourhoods and replacing them with towers and highways designed to modern specifications. Jacobs argued that the apparent disorder of old cities — the mix of uses, the short blocks, the aged buildings rented cheaply by small enterprises — was not a failure of planning but the condition for urban vitality. The city street, she said, is not merely a channel for traffic. It is a stage for social life, and its safety depends not on police but on the presence of people with a reason to be there at different hours of the day.
The planners she opposed believed that separation was rational: houses in one zone, offices in another, factories in a third, parks in a fourth. This produced cities that were orderly on a map and deadening on the ground. People drove between zones because nothing was walkable. Streets emptied at six in the evening. Parks, lacking the natural surveillance of mixed-use activity, became unsafe. The planned city worked as a diagram. It failed as a place.
Jacobs's central insight was that diversity — of uses, of ages of buildings, of people and their schedules — is a resource, not a problem. Concentration is not crowding; it is the condition for the spontaneous interactions that generate economic and social life. A city that is too orderly is a city that has been emptied of the conditions for its own renewal.
