To understand this structure, let us think abstractly for a moment, using numbers as symbols. Automatically, merely because relationships are established among the subsets once the subsets are chosen, the collection has a definite structure. Now, a collection of subsets which goes to make up such a picture is not merely an amorphous collection. In fact, I claim that whatever picture of the city someone has is defined precisely by the subsets he sees as units. Of the many, many fixed concrete subsets of the city which are the receptacles for its systems and can therefore be thought of as significant physical units, we usually single out a few for special consideration.

It derives its coherence as a unit both from the forces which hold its own elements together and from the dynamic coherence of the larger living system which includes it as a fixed invariant part. I define this fixed part as a unit of the city. It is the unchanging receptacle in which the changing parts of the system – people,newspapers, money and electrical impulses – can work together. The news rack, the traffic light and the sidewalk between them, related as they are, form the fixed part of the system. This effect makes the news rack and the traffic light interactive the news rack,the newspapers on it, the money going from people’s pockets to the dime slot,the people who stop at the light and read papers, the traffic light, the electric impulses which make the lights change, and the sidewalk which the people stand on form a system – they all work together.įrom the designer’s point of view, the physically unchanging part of this system is of special interest. Some of them just read the headlines, others actually buy a paper while they wait. When the light is red, people who are waiting to cross the street stand idly by the light and since they have nothing to do, they look at the papers displayed on the news rack which they can see from where they stand. In the entrance to the drugstore there is a news rack where the day’s papers are displayed.

When the elements of a set belong together because they co-operate or work together somehow, we call the set of elements a system.įor example, in Berkeley at the corner of Hearst and Euclid, there is a drugstore, and outside the drugstore a traffic light. Since, as designers, we are concerned with the physical living city and its physical backbone, we must naturally restrict ourselves to considering sets which are collections of material elements such as people, blades of grass, cars, molecules, houses, gardens, water pipes, the water molecules in them etc.

A set is a collection of elements which for some reason we think of as belonging together. In order to define such structures, let me first define the concept of a set. When compared with ancient cities that have acquired the patina of life, our modern attempts to create cities artificially are, from a human point of view, entirely unsuccessful.īoth the tree and the semi lattice are ways of thinking about how a large collection of many small systems goes to make up a large and complex system.More generally, they are both names for structures of sets. It is more and more widely recognized today that there is some essential ingredient missing from artificial cities. Levittown,Chandigarh and the British New Towns are examples of artificial cities. Siena, Liverpool, Kyoto, Manhattan are examples of natural cities. And I shall call those cities and parts of cities which have been deliberately created by designers and planners artificial cities.

I want to call those cities which have arisen more or less spontaneously over many, many years natural cities. In order to relate these abstract structures to the nature of the city, I must first make a simple distinction. I shall contrast it with another, more complex abstract structure called a semi lattice. The tree of my title is not a green tree with leaves.

Newsrack art