The City is not a Tree By Christopher Alexander

The City is not a Tree
By Christopher Alexander
Architectural Forum Vol 122 No 1 April 1965

p.58. The tree is “a name for a pattern of thought, The semi-lattice or the name for another more complex mode of thought.”

“It Is more and more widely recognised today that there is some essential ingredient missing from artificial cities.”

“I believe that a natural city has the organisation of a semi-lattice; but that when we organise a city artificially, we organise it as a tree.”

p.59 example of newstack by a drug store next to a traffic light. Folks stop at lights, buy newspaper. This makes a unit.

p.60 “It is this lack of structural complexity, characteristic of trees, which is crippling our conceptions of the city.”

Says gReater London plan 1943 by Abercroimbie and Foreshaw concerned by a large number of communities, increased segregation. Tree.

p. 62 “In a traditional society if you ask a man to name his best froends and then ask each of those in turn to name their best friends then they will name each other so that they form a group. A village is made of a number of separate closed groups of this kind. But today’s social structure is utterly different. If we ask a man to name his friends and then ask them in turn to name their friends they will all name different people, very unlikely unknown to the first person; these people would then name others and so on outwards. There are virtually no closed groups in modern society.”

May (second part of article)

p. 59 Le Corbusiee, Luis Kahn and others separate moving vehicles from pedestrians. “It’s not always a good idea. The urban taxi can function only because pedestrians and vehicles are not separated.”

p.60 remember four objects: orange, watermelon football, tennis ball. You do it in mind by grouping them but cannot imagine in mind all the possible groupings at same time. “In a single mental act you can only visualise a tree.
“The tree is accessible mentally and easy to deal with. The semi lattice is hard to keep before the mind’s eye and therefore hard to deal with.”

Says tendency of humans “when faced by a complex organisation, to reorganise it manetally in terms of non-overlapping units. The complexity of the semi-lattice is replaced by the simpler and more easily grasped tree form.”

p.61 “When we think in terms of trees we are trading the humanity and richness of the living city for a conceptual simplicity which benefits only designers, planners, administrators and developers.
“In a society dissociation is anarchy. In a person, dissociatioon is the mark of schizophrenia and impending suicide.”
Separate old people from young eg Sun City. Result of “tree like thought.”

“The city is not, cannot and must not be a tree. The city is a receptacle for life.”