A City Is Not A Tree
A City Is Not A Tree
A City Is Not A Tree
CHRISTOPHER ALEXANDER
I 119
slum dwellers and Zen architectural details into a Japanese school. He and his followers seek
architecture which is "alive"; architecture that possesses "the quality without a name."
Consider the relevance of J. B. Jackson's description of how the informal vernacular architecture
of small U.S. towns meets human needs (p. 82) to Alexander's conviction that built environments that
grow organically contain important lessons for planners. Alexander shares architectural critic Jane
Jacobs's love of apparently chaotic, jumbled urban neighborhoods. Like Jacobs he sees a complex
order and rationality behind an apparently disorderly facade. Consider Alexander's concept of a semilattice structure in relation to Jacobs's argument for designing streets to provide play space for
children, security, and areas for human interaction as well as space for cars to drive (p. 104). A casual
observer might consider the resulting street a confused and disorderly one. She might not see how
Editors' introduction
it meets multiple, complex human needs. Alexander would like to help architects and planners design
designs for the built environment elements reflecting underlying human psychological and spiritual
streets which achieve the positive qualities of lively streets in New York's Greenwich Village or Boston's
needs and cultural values. But none has broken so completely with conventional architectural
West End before urban renewal tidied up (and deadened) the streetscape. Note also the similarity to
practice and sought more deeply to make his designs reflect these fundamental values than Austrianborn, British-trained, U.S.-based architect/planner Christopher Alexander.
British architect/planner Raymond Unwin's respect for natural cities and for urban forms shaped by
Alexander is a self-proclaimed iconoclast, deliberately distancing himself from virtually all the
Alexander's theories are developed in a series of books published by Oxford University Press in
major mainstream currents of twentieth-century architectural and planning thought. It is notable that
New York: The Oregon Experiment (1975), A Pattern Language (1977), The Timeless Way of Building
the eight "treelike" plans he singles out for attack in the following selection represent a diverse set
(1979), The Linz Cafe (1981), The Production of Houses (1985), and A New Theory of Urban Design
17
of the most respected and famous twentieth-century plans from Le Corbusier's plan for the new town
(1987). An overview of his work by Ingrid F. King is "Christopher Alexander and Contemporary
of Chandigarh, India, based on his principles for a contemporary city (p. 368), to Paolo Soleri's
visionary megastructure of Mesa City in the Arizona desert (p. 454).
Since publication of his provocative early attack on the sterility of formal "treelike" city plans in the
following selection, Alexander has been engaged in a lifelong search to decipher the deep structures
underlying human needs and to define recurring patterns for a new paradigm of architecture. The
following selection is clear that a city should not be designed with a neatly branching treelike
organization dividing functions from each other. Alexander condemns tidy city plans which layout
discretely bounded neighborhoods, zone one area for housing and another for business, or establish
areas just for universities or cultural facilities. He sees human activity as much more complex and
overlapping than that.
Alexander's approach to describing how cities should be designed in this selection may trouble
readers who seek clear, rational guidelines. He takes the position that not enough is yet known about
how to design non-treelike cities to provide definite answers. Like an artist or a Zen master instructing
an apprentice, Alexander closes this selection with provocative analogies, examples, and metaphors.
He suggests how an individual might pursue the quest for good design, but he does not offer a stock
set of the answers.
During the past three decades Alexander and his colleagues and students at the Center for
Environmental Structure at the University of California, Berkeley have conducted a series of
"experiments" working to understand and demonstrate how to design cities which are not "trees."
Alexander's writings since "A City Is Not a Tree" provide an abundance of specific principles and
examples as well as many more unanswered questions and lines for exploration.
While Alexander is fascinated with physical form, his approach begins with an interactive process
working with clients to understand their most fundamental needs. Profoundly respectful of the ideas
of clients, Alexander's projects incorporate rammed earth and chicken wire into housing for Mexicali
life, our modern attempts to create cities artificially are, from a human point of view, entirely
unsuccessful.
Architects themselves admit more and more
freely that they really like living in old buildings
more than new ones. The non-art-Ioving public
at large, instead of being grateful to architects
for what they do, regards the onset of modern
buildings and modern cities everywhere as an
inevitable, rather sad piece of the larger fact that
the world is going to the dogs.
It is much too easy to say that these opinions
represent only. people's unwillingness to forget
the past, and their determination to be traditional. For myself, I trust this conservatism.
Americans are usually willing to move with the
times. Their growing reluctance to accept the
modern city evidently expresses a longing for
some real thing, something which for the
120
I CHRISTOPHER ALEXANDER
18
I 121
122
I CHRISTOPHER ALEXANDER
The structure illustrated in diagrams C and D in the following fact: a tree based on 20 eleis a tree. Since this axiom excludes the possibil- ments can contain at most 19 further subsets of
ity of overlapping sets, there is no way in which the 20, while a semi-lattice based on the same
the semi-lattice axiom can be violated, so that 20 elements can contain more than 1,000,000
every tree is a trivially simple semi-lattice.
different subsets.
However, in this paper we are not so much
This enormously greater variety is an index
concerned with the fact that a tree happens to be of the great structural complexity a semi-lattice
a semi-lattice, but with the difference between can have when compared with the structural
trees and those more general semi-lattices which simplicity of a tree. It is this lack of structural
are not trees because they do contain over- complexity, characteristic of trees, which is
lapping units. We are concerned with the differ- crippling our conceptions of the city.
ence between structures in which no overlap
To demonstrate, let us look at some modern
occurs, and those structures in which overlap conceptions of the city, each of which I shall
does occur.
show to be essentially a tree. It will perhaps be
It is not merely the overlap which makes the useful, while we look at these plans, to have a
distinction between the two important. Still little ditty in our minds:
more important is the fact that the semi-lattice
Big fleas have little fleas
is potentially a much more complex and subtle
Upon their back to bite 'em,
structure than a tree. We may see just how much
Little fleas have lesser fleas,
more complex a semi-lattice can be than a tree
And so ad infinitum.
19
newtown
loop
123456
123456
loop
~~
Ii\ Ii\ !l\ Ii\ Ii\ Ii\ !l\
petal neighborhoods
~~~~
houses
Figure 1
Figure 2 Columbia, Maryland, Community Research and Development Inc.: Neighborhoods, in clusters of five,
form "villages." Transportation joins the villages into a new town. The organization is a tree.
124
I CHRISTOPHER ALEXANDER
20
traditional SOCiety
!\
closed group
~'"O~
individuals
Figure 3
individuals
:126
I CHRISTOPHER ALEXANDER
Waterloo Road
neighborhood
boundary
:~:"1!J~,'"
Waterloo Road
neighborhood
///~
adjacent
neighborhood
adjacent
neighborhood
Figure 5
21
I :127
Cambrrdge
that of Goodman's Communitas, or Soleri's
Mesa City, which separate the university from
the rest of the city. Again, this has actually been
realized in common American form of the
isolated campus.
What is the reason for drawing a line in the
city so that everything within the boundary is
university, and everything outside is nonuniversity? It is conceptually clear. But does it
correspond to the realities of university life?
Certainly it is not the structure which occurs in
non-artificial university cities.
Take Cambridge University, for instance. At
coffee street
bus
boarding medical
certain points Trinity Street is physically almost college
shops
houses
school
indistinguishable from Trinity College. One
pedestrian crossover in the street is literally part Figure 6
of the college. The buildings on the street,
though they contain stores and coffee shops and
created its own familiar section of the city. In
banks at ground level, contain undergraduates'
Manhattan itself, Carnegie Hall and the Metrorooms in their upper stories. In many cases the
politan Opera House were not built side by side.
actual fabric of the street buildings melts into
Each found its own place, and now creates its
the fabric of the old college buildings so that one
own atmosphere. The influence of each overlaps
cannot be altered without the other.
the parts of the city which have been made
There will always be many systems of
activity where university life and city life unique to it.
The only reason that these functions have all
overlap: pub-crawling, coffee-drinking, the
been brought together in the Lincoln Center is
movies, walking from place to place. In some
that the concept of performing art links them to
cases whole departments may be actively
involved in the life of the city's inhabitauts (the one another.
But this tree, and the idea of a single hierhospital-cum-medical school is an example). In
archy of urban cores which is its parent, do not
Cambridge, a natural city where university and
illuminate the relations between art and city life.
city have grown together gradually, the physThey are merely born of the mania every simpleical units overlap because they are the physical
minded person has for putting things with the
residues of city systems and university systems
same name into the same basket.
which overlap (Figure 6).
The total separation of work from housing,
Let us look next at the hierarchy of urban
started by Tony Garnier in his industrial city,
cores, realized in Brasilia, Chandigarh, the
then incorporated in the 1929 Athens Charter,
MARS plan for London, and, most recently, in
is now found in every artificial city and accepted
the Manhattan Lincoln Center, where various
everywhere where zoning is enforced. Is this a
performing arts serving the population of
sound principle? It is easy to see how bad
greater New York have been gathered together
conditions at the beginning of the century
to form just one core.
prompted planners to try to get the dirty factoDoes a concert hall ask to be next to an
ries out of residential areas. But the separation
Opera House? Can the two feed on one
misses a variety of systems which require, for
another? Will anybody ever visit them both,
gluttonously, in a single evening, or even buy their sustenance, little parts of both.
Jane Jacobs describes the growth of backyard
tickets from one after going to a concert in the
industries in Brooklyn. A man who wants to
other? In Vienna, London, Paris, each of the
start a small business needs space, which he is
performing arts has found its own place,
very likely to have in his own backyard. He also
because all are not mixed randomly. Each has
128
I CHRISTOPHER ALEXANDER
22
1\
small
orange
+ tennis ball +
watermelon
Figure 7
football
orange
larger
tennis ball
football
130
I CHRISTOPHER ALEXANDER
23
Figure 8
1234567
123456
134567
234567
Figure 9
elements are the first signs of coming destruction. In a society, dissociation is anarchy. In a
person, dissociation is the mark of schizophrenia and impending suicide. An ominous
example of a city-wide dissociation is the separation of retired people from the rest of urban
life, caused by the growth of desert cities for the
old such as Sun City, Arizona. This separation is
possible only under the influence of tree-like
thought.
It not only takes from the young the company of those who have lived long, but, worse,
causes the same rift inside each individual life.
As you will pass into Sun City, and into old age,
your ties with your own past will be unacknowl-