A CITY IS NOT A TREE
A CITY IS NOT A TREE
By Christopher Alexander
ABOUT THE AUTHOR
Christopher Wolfgang Alexander (born: 4th October 1936, in Vienna, Austria) is a widely influential British-American architect, design theorist, and currently a professor of Architecture at the University of California, Berkeley.
As a theorist, teacher, author, practicing architect, and builder, Alexander has taken it upon himself to question everything, from construction details and the effects of color to the process by which a global species makes and remakes its environment and, beyond, to the objective bases of beauty itself. Questions like, what is an architect? What is a good building? Should architects strive for beauty in their work? What is beauty? Christopher Alexander has explored such fundamental questions in greater depth or breadth, or with greater persistence, clarity, and originality of thought.
His theories about the nature of human-centered design have affected fields beyond architecture, including urban design, software, sociology and others. Alexander has designed and personally built over 100 buildings, both as an architect and a general contractor.
In architecture, Alexander's work is used by a number of different contemporary architectural communities of practice, including the New Urbanist movement (New Urbanism is an urban design movement which promotes environmentally friendly habits by creating walkable neighborhoods containing a wide range of housing and job types. It arose in the United States in the early 1980s) to help people to reclaim control over their own built environment.
He is also known for many books on design and process, like The timeless way of building (This book leads anyone who looks for it to buildings which are themselves as ancient in their form, as the trees and hills, and as our faces are), A pattern language: Towns, Buildings, Construction (The book provides rules and pictures, and leaves decisions to be taken from the precise environment of the project. It describes exact methods for constructing practical, safe and attractive designs at every scale, from entire regions, through cities, neighborhoods, gardens, buildings, rooms, built-in furniture, and fixtures down to the level of doorknobs), The nature of order, The Oregon experiment, Notes on the Synthesis of Form: A City is Not a Tree.
For more than 30 years, Alexander's work has challenged architects to delve deeper, to serve the needs of the body and spirit in a way that photography cannot capture, a way that must be experienced directly. In his architectural practice he has shown a way to create, without being merely imitative, buildings with the richness, resonance, and life we are accustomed to experiencing only in old buildings.
INTRODUCTION
WHAT IS A CITY?
According to alexander there are two types of cities-
Cities that have developed organically over a period of many years are called as natural cities. These cities have life. E.g. Siena, Kyoto, Manhattan, etc.
Cities that are deliberately created by designers and planners are called as planned cities. The modern attempts to create cities artificially are, from a human point of view, entirely unsuccessful According to the author these cities lack the essence of life. E.g. Chandigarh, British New Towns, Levittown, etc.
UNDERSTANDING TREE AND SEMI LATTICE
A set is a collection of elements which for some reason we think of as belonging together.
To understand the structure of tree and semi lattice structure, let us consider a simpler structure made of just half a dozen elements. Label these elements 1,2,3,4,5,6. Not including the
full set [1,2,3,4,5,6], the empty set [-], and the one-element sets [1],[2],[3],C4],[5], [6], there are 56 different subsets we can pick from six elements.
SEMI LATTICE: Sets which overlap, like [123] and [234]. Here, it meets only certain conditions or overlaps. His semi lattice axion goes like, “A collection of sets forms a semi lattice if and only if, when two overlapping sets belong to the collection, the set of elements common to both also belongs to the collection.”
TREE: Sets which are either entirely part of larger sets like [34] being a part of [345] and [3456] or entirely disjoint of each other, like [123] and [45]. No overlaps. Here, the structure meets more restrictive conditions. His tree axiom goes like, “A collection of sets forms a tree if and only if, for any two sets that belong to the collection either one is wholly contained in the other, or else they are wholly disjoint.”
EXAMPLE OF SEMI LATTICE
The author gives an example of a street in Berkeley at the corner of Hearst and Euclid. There is a drugstore, and outside the drugstore a traffic light. At the entrance to the drugstore there is a news rack where the day's papers are displayed. 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. Some of them just read the headlines, others actually buy a paper while they wait. 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.
The news rack, the traffic light and the sidewalk between them, related as they are, form the fixed part of the system. It is the unchanging receptacle in which the changing parts of the system - people, newspapers, money and electrical impulses - can work together. I define this fixed part as a unit of the city.
In case of this example, one unit consists of news rack, sidewalk and traffic light. Another unit consists of the drugstore itself, with its entry and the news rack. The two units overlap in the news rack. Clearly this area of overlap is itself a recognizable unit and so satisfies the axiom above which defines the characteristics of a semilattice.
CHICAGO’S EL TRAIN MAP
The CTA train lines form a very simple Tree, with the downtown Loop serving as the central “common element” for the city and each line reaching out to one set of neighborhoods.
- The Brown and Red Lines connect the Loop to the north neighborhoods and to the Yellow and Purple Lines in the nearest north suburbs.
- The Green and Red Lines connect neighborhoods south of the Loop to downtown but do not connect southern suburbs
- The Blue, Green, and Pink Lines serve neighborhoods west from the Loop, and each extends into the very near west suburbs.
- The Orange and Blue Lines run through the Southwest and Northwest segments of the city, respectively, and connect the two major airports to the Loop and the public transit system
The interstates and highways connecting the City of Chicago to its greater suburban region echo the structure of the El trains — radiating outwards from the Loop in Tree-like fashion.
TREE - STRUCTURE AND RESTRICTED MOBILITY
As a larger city, Chicago’s physical connections form a tree. The most mobile we can be is if we live, work, and play along a single branch, a structure that separates us from those people living, working, and playing along the other branches.
EXAMPLES OF CITY AS A TREE
- Each of these structures, is a tree.
- Each unit in each tree that has been described is the fixed, unchanging residue of some system in the living city.
- Like for example, just as a house is the residue of the interactions between the members of a family, their emotions and their belongings; and a freeway is the residue of movement and commercial exchange
- However, in every city there are thousands, even millions, of times as many more systems at work whose physical residue does not appear as a unit in these tree structures
- The units which do appear fail to correspond to any living reality; and the real systems, whose existence actually makes the city live, have been provided with no physical receptacle
- So, what are its disadvantages ?
- takes from the young the company of those who have lived long.
- causes the same rift inside each individual life.
- as you pass into Sun City, and into old age, your ties with your own past will be unacknowledged, lost and therefore broken.
- your youth will no longer be alive in your old age.
- eventually your life will be cut in two.
- The semi-lattice is hard to keep before the mind's eye and therefore hard to deal with.
- Grouping and categorization are among the most primitive psychological processes.
- Because the mind's first function is to reduce the ambiguity and overlap in a confusing situation and because, to this end, it is endowed with a basic intolerance for ambiguity - that structures like the city, which do require overlapping sets within them, are nevertheless persistently conceived as trees.
CONCLUSION
- A city cannot be a tree-structure where functions and objects are strongly disintegrated and rearranged into blocks or groups, isolated from the adjoining object.
- It needs to have overlaps in-order to have spontaneity and life. But, overlap doesn't alone give structure, it might also give chaos. To have structure, we need to have the right overlap. This is very important.
- Perhaps we build and renovate our streets with room for bikes to fluidly share these pathways with cars, buses and taxis.
- Perhaps, we consider pedestrian traffic when organizing neighborhoods and thoroughfares.
- Perhaps we promote the co-existence of residence and business.
- We must align our homes with our lives.
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