The Hulls of Public Space
From The Nature of Order, Book III, Chpt Three

By Christopher Alexander

This chapter contains examples of living process creating belonging, first, in the public worlds of cities. The chapter gives examples of the creation of the now-damaged core structure of every environment: a coherent structure of public space, continuous, pleasant, connected, and coherent—and above all, positive, which forms the backbone of a living community.

Section 1: The Unfolding of Public Space

When living processes are applied systematically, step by step, to the public space in a human community they will—because of their powerful emphasis on the formation of strong centers—generate a system of articulated, positive, mainly pedestrian spaces.

Whether in unplanned construction or in a planned form, living processes do this because, when it they are genuinely being used, they form positively shaped, coherent, strong centers of space, one by one, in real time and space, through the unfolding of local symmetries. These centers have the chance, then, to become differentiated living entities, each with its own enclosure, its own character, its dependency on the people who pass through and congregate.

I choose to call these coherent, partly enclosed public spaces, especially when they are positively shaped, the HULLS of public space. Each is like a boat, or like the shell of a nut, what in German is called die Hülle, each one holding and forming a kernel of interior space contained. The hulls are the only spaces which can give communal structure to a town or to a neighborhood.

One of the greatest defects in 20th-century cities was the loss of nearly all awareness of the shape, character, existence, and creation of public space, its enormous public impact and importance. The word "hull" draws attention to these spaces, it helps to make them more solid in our awareness. Above all it encourages us to remember that public space must always be POSITIVE.

Section 2: Positive Space

What is POSITIVE SPACE? What is it like when space becomes positive? How do you recognize positive space when you see it? The answer is that it depends on the density of STRONG CENTERS in the space. Outdoor space is positive when it is shaped, just as a room is shaped. It has a contained character; it is bounded by walls, trees, fences, natural vegetation, enclosure of some kind. When space is positive, passing through it one moves from space to space, as if one were moving through a series of rooms. Each space, individually, is a strong center, each one has a BOUNDARY, one feels its heart, its substance; and one passes from one of these strong centers, to the next, as one moves around and though the space. This is entirely different from the space of present-day America—where a loose aggregation of parking lots, asphalt, wide roads, yards without significant meaning and therefore without significant boundaries, causes an amorphous substance to exist. A great deal of the nature and meaning of positive space may be seen in a plan drawing, with reference to black and white. When we look at a place which has positive space, if we see the plan in which space is drawn white, and the rest black, then the white spaces have a feeling almost as if they are carved out, literally, from the solid rock, like a series of caves, connected by tunnels. When we reverse the black and white (just by taking the negative of the picture), we get the spaces black, and the rest white; now, when it is good, the space looks almost like a series of buildings or halls, connected by passages.

In the Nolli plan, the space consists of squares, streets, and churches. These are the public spaces. The dark part of the drawing refers to all the buildings (private ones), and includes also all the private gardens, not accessible to the public. So one sees with enormous clarity the beautiful hull-like character of the public space.

How do you then, make this positive space? In the case of Rome, we are looking at the trace of a process that went on for nearly 2000 years (the plan was drawn at the beginning of the 18th century). We are looking at the trace of a process by which the inhabitants of Rome, gradually, step by step, made each bit of space more and more positive. This happened because (as explained in Book 2), the traditional process allowed a continuous structure-preserving process to occur, which created and embellished strong centers continuously. As each alley, each plaza was shaped, it was then shaped and re-shaped by insertion and corrections. Most of these will have created new centers; so, not only the positive shapes of the squares and alleys and churches.. but the individual centers, within the space, by being made stronger, then created GOOD SHAPE in every space; so the Piazza Navona is a beautiful shape, the alley gets a thickening at the Y where another alley forks off, the small square that starts amorphous, gets a cafe in one corner… when the next modification in the building fronts occurs, this cafe is harbored, nestled, it forms a new strong center, and then, suddenly, the shape of the main square in which it is sitting has received another center (in this one corner) and the shape of the whole square is now more positive.

One by one, all the fifteen properties get unfolded to make the space; ECHOES comes about, in natural similarities which occur at similar places in the whole; GRADIENTS occur as one moves away from the main spaces, and towards them, in the fabric, and in Nolli plan we see these gradients reflected, for example, in the widening shape of paths that approach the squares. DEEP INTERLOCK AND AMBIGUITY occurs at BOUNDARIES and at the edge of spaces; we see it, in this case in the church porticos visible in the Nolli plan. LOCAL SYMMETRIES occur, of course, and are visible throughout the fabric of the space. To a first approximation, almost every one of the spaces and sub-spaces, has symmetries and local symmetries defining it. Subsidiary to the local symmetries we see ROUGHNESS in the shape of almost every piece of urban space, since the influences of tradition, previous construction, topography all modify the whole, and make the simple shapes more complex.

LEVELS OF SCALE occur, of course, in the hierarchy of sizes we see in the exterior space, in the many different-sized centers which are formed through the unfolding, and then is chiefly embodied in the way that many spaces are defined by small spaces opening into them. INNER CALM and NOT SEPARATENESS.

As the formation of positive space matures, all these properties appear, and the space slowly gets its living character, just as buildings and objects can have. It is this living space, endowed with the properties, endowed therefore with living centers, that forms the effective and useful hull of urban space, to support society.

Section 3: How Hulls of Public Space Come Naturally from Structure-Preserving Transformations

Let us now pass to the general case, the part of a town in our time, and the kinds of process through which positive hulls of public space may be formed. Assume that we have an open attitude to a town, or neighborhood. By that I mean that we are able to consider the wholeness of a given place, as it is, without prejudice about what is or is not possible. We are mentally open to the wholeness, can therefore afford to allow—mentally—unfolding to occur.

There will usually be some rather natural places for social space to be created. These latent centers may arise as a result of a certain density, where there is a natural need for places of congregation: thus, in a fairly natural way, at the center of gravity of a population, there may be a push towards a void to occur, a center, which gathers together the activities of that population into itself.

And there are sometimes naturally occurring spots of natural beauty, which call a hull of space into being, just because they point to the importance of such a particular spot in the land (or in the town) as a natural center which has importance in people's hearts.

Or, if the community has formed a collective vision which has—in addition—identified naturally required generic centers of some particular type, then these generic centers, too, might induce, from within the culture, a natural pressure towards the creation of such space.

Best of all, for the unfolding, is when these processes, all three of them, coincide to identify particular, and obvious places, which the people in the community recognize as "Of course, we always felt there should be something there…"

The answer comes, again and again, from the fundamental process. Whatever living process is at work, it is made up of repeated application of the fundamental process. The fundamental process strengthens centers. Strong centers, as they form, form positive space.

Section 4: Shaped Public Space Forming Living Centers

Imagine, then, that we are to embark on a program of construction which makes a part of a town into a system of public places entirely made of POSITIVE SPACE, or think of it as "solid space". That means, really, that each part of the downtown, and each part of each neighborhood, is to be a strong center. In our ideal city, when we are finished, there are to be no places that are not living centers. This will be true of each part—each center—in the downtown area; there is to be nothing left over.

Some of these solid spaces may be parts of a sidewalk—I do not say sidewalks—because I mean only a single piece of a sidewalk, which is a graspable, felt, solid object of space, where I want to be. When I leave that place, I go to another one.

Obviously there may be avenues, a focal point, a small square, long pieces of sidewalk flanked by shops, a short wide segment of sidewalk or paving where there are pigeons. There are also—perhaps, lawns; there can be a sidewalk cafe—an area of tables and chairs, bounded; there could be an area of umbrellas. And, certainly, there will be less intense parts, but always positive space and THE VOID and BOUNDARIES, forming the background against which the many more intense small volumes of space are a counterpoint. But even the void is itself a place, solid, continuous, empty, bounded, visible, and felt as the void.

Against all this in our process of forming space in the city, we must most carefully make the right kind of space for cars, parking lots, parked cars, moving in and out of parking. Our modern destroyed space has come about largely because with the onset of cars, 2000 years of tradition about forming pedestrian, horse and carriage space, suddenly dissolved—became irrelevant—and we have hardly yet found a new tradition in which the rules of the game—the patterns, the generic types of centers for parking, cars, movement of cars, deliveries, is clear and worked out in relation to the hulls of public pedestrian space.

The temptation to say—keep the cars out, make it all pedestrian—is too harsh. In some cases, it is just the cars which create the life; the freedom of access that they permit which brings vivacity, energy, imagination. But undoubtedly, the pure pedestrian space in which there are no cars is also vital, to walk, dream, play, unhurried and uninterrupted.

So, in support of the emergent unfolding of the hulls of public space, we need a specific group of patterns, or generic centers, that tell us how the cars are going to work. How much parking is there. How visible or invisible. How is it to be paid for. What density is to be allowed.

Section 5: The Spine Structure of the Eishin Campus

The Eishin campus, built 1985, is a pedestrian world which really works. It has an atmosphere of calm, one feels oneself there; it is calm and nourishing to the spirit. After it was built, though it is a school and college, the head of the school, instead of head or chairman, is called the mayor of Higashino. This was a tribute, I think, to the calm and living atmosphere of the place.

At its core is the pedestrian hull. In this instance, we created such a skeleton, or hull, after a year of discussion with the faculty. It contains streets, gates, a lake, streets around a lake, a bridge. The hull provides the campus its core, in which people feel at home, and against which, later, they designed and we built, the individual buildings of the campus.

The unfolding which took place in this project was that, first, a system of public space was identified, and then we tried to make sure that every part of the Eishin campus came into being and was related to the land by structure-preserving transformations.

The success of this world is, in my view, entirely given by the beauty of the hull, the public hull we identified and built. It creates a world where people enjoy walking about: bridges, paths, avenues of trees, gates, gardens, doorways, stairs: it is a connected world, not kept too isolated from cars, but still a protected and peaceful world which works.

Section 6: The Hulls for a Community of Families in Texas: Unexpected Centers in a Piece of Land

In this instance the area covered is small: a few acres, designed to serve five houses, with a lot of brush around the edges. However, the formation of public land, and the hull of public space which is formed there, provides, in microcosm, a view of how this works at every scale.

My colleagues and I had just begun work to build five houses on Lake Travis, in Austin, Texas. Almost within minutes of our first seeing the land, a certain structure became visible. This visible structure was the wholeness of the land—as it was then, in 1992. It included a swath of trees running down towards the water, a communal structure, which defined the heart of the land. It had a highly complex shape. My colleagues and I defined it carefully, observed it, marked it with stakes in the land. The next day, we took the families to the land, and showed it to them, explained that it would be best to reinforce this latent communal system of centers that lay in the land, and make the individual houses have their relation to it.

It was a simple idea. Family members were shocked, at first, and described themselves as deeply moved. As we stood under one grove of trees, Linda said that she had seen these trees many times before, but never before noticed that there were these natural centers there: that seeing them completely altered her relation to the land.

Merely defining this structure of land, water and trees, just identifying it and bringing it out into the open, allowed everyone to have a more excited, animated, substantial and feeling-filled relation to the activity of choosing, and placing their houses. Suddenly, instead of merely putting each house in a random arrangement of vegetation on arbitrarily divided pieces of land, the house could be placed in relation to an understood and meaningful public structure, which made sense, deeply, and which allowed the act of placing each house to make sense too.

I talked to them about the basic principle of all architecture leaving the structure which exists, helping it, reinforcing it—and that making even tiny changes too casually can be damaging. It was the wholeness of the land, which already existed there, that guided us. The families spoke often about the way that they were moved by their awareness of this whole, that it corresponded to their intuitive knowledge, but that raising it to the level of a conscious principle was an enormous help to them. Apparently they became deeply moved by the desire to protect and extend and enlarge the wholeness of the land, and by the principle that every act must be done to increase the chance of doing this.

The common land we had identified as a coherent shape, of course then became—through our construction—the public hull which, later, allowed these houses to come to life. We shaped it carefully, gave it a BOUNDARY (in the form of a low stone wall running hundreds of feet around this common land); we gave it STRONG CENTERS (in the form of a seat with a fountain at the upper end, and a trellis, fountain, and bench at the lower end overlooking the lake). We gave the heart of it a powerful feeling of THE VOID (by keeping it uncomplicated, uncluttered). We allowed LEVELS OF SCALE to form there, by making the individual old trees, and the entrances to houses, and the top end and lower end, into smaller centers in their own right. We used LOCAL SYMMETRIES in the formation of local areas like the entrance to the hull, and the paths which we formed within it. We allowed ROUGHNESS to dominate, in the way the wall, for instance, follows the ground, not stepping too carefully, but falling naturally with the terrain. The design of this long egg-shaped land was dominated, too, by GRADIENTS in the land.

Section 7: Shaping the Hulls for Part of a New Town in Greater Frankfurt

The next example illustrates a case from a part of a big city. In 1996 I was asked to create a small quarter of a new part of the town of Hoechst, a part of greater Frankfurt: this was a new quarter destined to be worker housing for the factory workers of Hoechst Pharmaceutical, the huge chemical company. Hajo Neis joined me, in this instance, as an independent partner. The land for our part of the town of Hoechst was an area of about two city blocks: we were to lay this out in such a way as to create both the space and the buildings, for 3- and 4-story worker apartments. I will explain how we managed the initial creation of the space.

To start with, we were given two roads forming a T-junction, given by the master plan.

We began by asking ourselves how these two roads could become positive space, even while carrying cars and traffic through the area. We asked our assistants and students to form a series of volumes for the buildings, and the volumes were then placed so as to make each of the two main parts of the T as strong as possible.

Knowing that we wanted the buildings to have good daylight in them, hence narrow wings of light, to include only narrow wings of light, thus creating ample daylight for the apartments, these early sketch-volumes already contained courtyards, so that the buildings were donut-like.

Here is the T, illustrated as it was originally given to us. Next to it, is the formation of volumes, we proposed, to shape the space positively.

Then we began to articulate the space by building paper models of the building volumes. We see how the space gets shaped: at the entrance we place an archway: at the closing end of the main space there is a narrowing, from each side, making the whole more contained.

There was one moment in the process, where our concentration on the space itself reached maximum intensity. I asked our students and apprentices to make a model, in which only the space existed. In this model there were no buildings, we used cardboard walls to enclose (hence form) space, and the cardboard represented the edges of buildings which might be capable of forming the space. But we were not tied to building shapes, at this early stage, and did not imagine any actual building volumes.

These models were made at 1/8th scale (1:100). We used cardboard to form the spaces, and I asked the students to keep adjusting the walls, until the space—each of the individual spaces, one by one—was really good.

The most interesting and important thing which emerged from this phase, was the secondary system of narrow paths, which connected courtyards, and formed a secondary grid, thus making the overall patterns of space, coherent, and truly fascinating. When one bent down, we could see all the way through these narrow streets, going from courtyard to courtyard, making the whole thing connected, cool, and beautiful.

The way this modeling process worked, it allowed us then to react to the quality of the space. We did this by looking into the model—which was first made at 1:100, looking through it, as if we were walking through, and modifying it as we worked. I noticed that the smaller streets—as one experienced them—made everything far more connected.

When we looked at the space of the project as a whole, and the overall three-dimensional pattern of this space, we could see that the system of secondary narrow streets connecting the courtyards, and functioning as a backup system to the main spaces of the larger streets, enormously increased the life of the thing. Every bit of space became more animated.

It was really only then, after that, once we had that structure in the space, that we began the detailed design of buildings. So, the hulls of space in this case—indeed, nearly all the components of this complex spatial structure—were almost fully formed, before we began to design and shape the buildings.

We now began to make the buildings, with an eye to position of entrances, to be sure that the entrances reinforce the overall way in which the space worked. But again, even then, we worked all the time so that the shape and plan of the buildings helped make the larger outdoor spaces even more powerful. For example, going back to the wider of the two main streets: it occurred to me that the sidewalk should be wide—not split equally between the two sides of the street, but all concentrated on one side, really wide, perhaps with grass on it. At first it seemed obvious that the wide sidewalk should be on the north of the street, where the sun would hit it most of the time. However, an experiment in Oakland, California, strongly changed our view.

All this may be described as a process in which we tried to make these two main arms of the T, as positive as possible, as living centers.

Following the fundamental process, we began to shape this T-junction in such a way as to intensify the existence of the main centers: by forming partial enclosure. To do this we undertook experiments in real city spaces that approximated the ones we were trying to define.

We found several places in Oakland (where we were working on the project, even though thousands of miles from Germany). Luckily the light conditions were not too different, so we could still imagine the German conditions. We looked hard, to start with, for a street oriented across the light (running East-west, and with a three story building along the north side) just like the situation in our Frankfurt plan. We set up markers, so that we could visualize the length accurately. Then, by standing across the street, to the south, we could imagine how wide the street should be. One had only to step forward, step back, using ones hands, sometimes using other people to mark edges, until one formed a picture of the real thing, as it would be, and could judge the best width for it. It was quite clear that it needed to be about 18 meters. 20 meters was too wide. 16 meters was too narrow.

Then, I noticed that the sun was too bright to look at in this configuration, when one was on the north side looking south, and that one felt more comfortable on the south side looking north. It was more comfortable looking at the north building which was illuminated by south light, than looking south staring directly into the sun. That meant we put the wide sidewalk on the south side of the street.

There were several of us making these judgments, together. That always helped to make our judgment more certain. With some effort, we could reach agreement of feeling on the issue.

Once the 18-meter width was fixed, we tried to find another place, to help us decide the width of the smaller street coming in from the south, to form the T. Again we looked for real places (still in Oakland) which approximated the size, height, and orientation to the sun of such a small street coming in from the south, into a wider street some 18 to 20 meters wide. From this work we were able to determine that the smaller one coming in should be no more than 9 meters wide: in fact we found out, by these thought-experiments, walking about and using the real place as a kind of simulation, that the street coming in should be wider at the mouth, and then narrower further back to the south. We determined—again by experiments based on feeling, and once again with several people doing it—that this minor one should be no more than 9 meters wide inside, with a slight widening at the mouth (about 11 meters wide).

It is not so easy to do these experiments. Although having several people together helps, because one can then get confirmation, and unity of judgement, it is not something anyone can do. The reason is, that it takes quite a lot of concentration, to keep on thinking about the real situation (in Frankfurt, and in our evolving cardboard model), while making these judgments in Oakland. One has constantly, to realize that it is an experiment about Frankfurt, and an experiment about the evolving design, which does not exist yet. That takes experience, and concentration. But it is possible, and it is tremendously useful. After doing it, one feels more certain about the design. Experience has shown often that this confidence is reliable, not misplaced. After such an experiment, the real places we build do have—often, or nearly always—the right feeling, a wonderful feeling. When it is done right, there is carry-over from the experiment to the real thing one builds.

If I had to define the process we followed as a generalized (and reusable) stepwise process, I might suggest that we follow a sequence of steps something like this:

  • 1. Identify the main spaces (in this case the T).
  • 2. Reshape these main spaces to strengthen them.
  • 3. Work out tentative buildings volumes to make these spaces stronger.
  • 4. Introduce inner spaces (gardens and courtyards) as the focus of the buildings.
  • 5. Make a model of the space alone.
  • 6. Add smaller passages, connecting the space and making it alive and varied.
  • 7. Establish the best orientation of minor centers (like the wide sidewalk, and neck of the smaller street).
  • 8. Fix the dimensions of the space (in relation to building heights which will be coming).
  • 9. Reconfigure the buildings so as to intensify the system of spaces.
  • 10. Grapple with building entrance positions, to support the spaces and the lines of movement. Locate further small centers (the narrow neck, the gate, the wider mouth of the small street).
  • 11. Subdivide the interiors, to fit the irregular building plans.

Make the interior plans of the buildings, fit the profiles and plans that have been evolved to strengthen the spaces. Each of these steps was a structure-preserving step, which forms, or strengthens centers. We took the steps, very deliberately, concentrating on only one center at a time. At each step we chose, as far as possible, the one thing which did most, at this step, to preserve and deepen the structure of the whole.

Expressed in other language, we worked to try and get each one to do the most to increase the feeling of that place.

In a later stage of work, we determined that the buildings were all to be courtyard buildings—necessary to get good light in the buildings—and the buildings around the courtyards had therefore to be very narrow.

Then, each of these gardens and courtyards was shaped to give it a powerful interior shape, without in any way distorting what in the buildings and entrances.

On the basis of many discoveries in the detailed design of the buildings, further refinements were made. The exact shape of two upstairs courtyards, the size of courtyard required by fire laws, the position of gates and walkways, were all adjusted to produce the final form.

Illustrations on these pages show how these hulls were formed. The work was done against the backdrop of buildings built, years ago, by Peter Behrens,which in another part of the Hoechst complex had begun to form other, similar hulls of space.

It is the whole of this structure of space, all the space that is shown black and solid in this diagram, which forms the hull that is to be built.

Again and again, the definition of the buildings came afterwards, after the space has been defined. The main job the buildings have, is to form the space.

Section 8: A New Approach to Urban Space: First Forming a Three-Dimensional Plan of Hulls as the Basis for All Construction of Individual Buildings

Let us ask, now, how this system of hulls—the shaped space of a town—might be created in practice. Since it is true that such space is hard to shape, and that shaping it must come first, before shaping buildings—then there must be some way of giving the creation of this system of hulls the mental and social priority it needs, then using it as a common goal for the town, and getting all the individual acts of construction to participate and complete the geometry of the spaces.

That, in turn, requires a new form of representation; a new form of plan or diagram. It must be something which is three dimensional, which is flexible (so that it can absorb the variations and local needs of different building projects); yet something which maintains a real handle on the shape of the space, and on the shaped system of spaces, that are required to keep the hulls of space throughout the town in good order.

I used to think that this large scale structure—the hulls of space for a town—had to be created piecemeal, as a forest is created from the growth and interaction of the trees, without a plan. I have become convinced, though, after years of trying to make it work, that it is after all necessary to have some kind of plan. Pure piecemeal growth just does not work well enough to create the wholeness we need in the city. The reason is, that it is the large-scale organization of the space, the actual geometric order of the streets and spaces, which matters most.

Even the beautiful and sentimental Italian hill-towns, which look as though they just "grew", were sometimes planned, laid out, by the bishop of the local church, or by someone else who cared about the whole.

The unfolding process, in the case of a town, is complex and difficult. It cannot always go on, romantically, "by itself". It needs guidance of a disciplined kind, through which the emerging space is defined, agreed, and visualized in some public and sharable form of a three-dimensional model. Once we have a way of doing this, the whole thing can go forward easily enough.

I show here a kind of diagram which may be useful: a three dimensional cartoon, which places emphasis on the spaces as solid objects, and allows everything else to support these spaces and related to them.

The principle which creates such hulls for the city as a whole, or for a large part of a city, may also be used repeatedly in local areas to create a similar map, or diagram, for the streets and pedestrian hull within each local area.

Section 9: Implementation

As I have said earlier in this chapter, I have found in all the years of my professional life that the shape of public space needs to be taken as seriously as the shapes of buildings, but this is very hard to implement, because our present consciousness focuses more easily on building-volumes, than on spaces. Above all, it means that our method of visualizing, or agreeing, on what we want to build, has to be thought through again.

In my experience, codes or systems of rules are unlikely ever to be enough. They are too abstract, too conceptual. They seek to be general—in the hope of creating a framework of order in which genuine freedom can exist. But in fact they do not say enough about the space, and do not guarantee the emergence of shaped space with genuine deep feeling—hence life.

This means that plans like zoning ordinances and master plans cannot be enough. They are not physical enough, they do not describe the attributes or necessities of living space, they do not insist with sufficient force and artistic clarity, on the actual shape of space. What is needed to support the individual acts of construction that make up the life of the town, is a three-dimensional diagram of the actual shape of the needed space.

A very physical document of the positive space—more physical even than a model—which shows in great detail the connections, shape, subtlety and physical presence of the space which is to be created, the interlock of spaces, the flow of space.

This plan could look like the three dimensional drawing of Samarkand: or the plan of Eishin, which has been staked on the ground, and is understood by everyone. Hosoi's comment, at the stage when only stakes were in the ground: "We could see.. the buildings.. standing there."

Once we have this diagram—it is an understanding, and agreement, a vision, which each player is then to help embody.

A major change; this process requires wide acceptance, throughout society, of an attitude in which transportation engineers have secondary—not primary—control over the shaping of roads. Transportation engineers must make their work on cars, subsidiary, to the work which defines the pedestrian hulls as places which people can use, and own. Even a street becomes a living room. In an unfolded world we find that all living structure is anchored by a hierarchy of circulation and living rooms. The common living rooms are shaped by buildings, by the exterior volumes of buildings. Every space that exists is either a public space, which is a hull, or a private space which forms a positive and useful garden.

We ask then, that each player makes a contribution to this growing whole.

We cannot legislate this. Rules, laws, restrictions, are too exact, too restrictive. Instead we ask that each individual actor think about it, work within it, contribute to it.

What we understand is a scheme of wholes. The remaining acts of construction are then to be like brush-strokes, which will gradually complete the painting. We know that some brush strokes, by virtue of their feeling, or their force, will themselves transform the vision of the whole. Still, though, it is the whole which is being conceived, like a sculpture of living space.

Section 10: Why the Fundamental Process Forms Hulls of Space

I should like to make you understand why just this structure—a system of hulls of public space—is created by the unfolding of a living process?

Consider the situation. Imagine at any step we have one positive space which is forming part of the hull. As I have said, these positive spaces have the quality that they open into one another, one into the next. Imagine, then, one step in the unfolding process. One of the places in the growing hull—one center—is to be made better, more living. To accomplish that, it is first to be better shaped itself. At the same time some larger center that it belongs to, is to be made stronger also—that will, often be the next space, the next larger space from which this one buds off like a limb-bud.

At the same time, the small center we started with is also to be strengthened by the formation of some smaller center. That means either a smaller symmetrical space—even an arch, gate, or doorway leading into it—or some detailed local symmetrical center which adds to the center that has already been formed: a fountain, a seat, perhaps something very elaborate in the middle, perhaps no more than a stone placed beside an old tree trunk.

Repeating this process, moving from center to center within the hulls of space, we see that with time, inevitably, step by step, just that structure which I have described, will be created.

Section 11: The Morphological Invariants Created by Living Processes at Work in the Public Realm

When public space unfolds under the impact of a fundamental process, the following features are likely to emerge:

The public space is gradually transformed to become a continuous, connected system of distinct centers, well-shaped, partly surrounded, enclosed, positive spaces. The centers include, but are not dominated by, what we now think of as streets—those spaces which allow cars to go in them.

To give them their definition, each of these public spaces is a center surrounded by buildings, by walls, by trees, by natural contours, even views. As a center, each is of them is visibly contained to make it a hull.

All activity opens from these hulls. The effect of the hulls, then, is rather like what was described in A PATTERN LANGUAGE as CIRCULATION REALMS: a system of closed precincts opening off one another, and so arranged that everything important opens off one of them.

When the fundamental process is working properly, the hulls will be more open than courtyards. But they will not be amorphous like modern streets. They will, rather, turn out composed of pieces of space, and each piece is a place where it is pleasant to be.

The way the spaces develop naturally under the impact of the fundamental process, it become clear that they belong to people. Each one is thought, felt, judged, given its dimensions in the place itself, by people standing in the place, using their common sense, their instinct, their sense of rightness. For each one, its size, diameter, length, width, edges, height of the edges… these are all formed while people are standing there, so that each place gets its feeling of centeredness.

Further, the whole thing is based, in some way, on natural features in the landscape, or in the townscape. It expands what is there, what is familiar.

These marked, defined centers, form the whole of the system of public space in the environment. We move from one to the next, there is nothing "left-over."

What can we say about the detailed geometry of the hulls? What strikes, above all, are the local symmetries, and complex syncopated smaller symmetries, modifying the larger ones in asymmetric fashion.

All parts of the unfolded public space are shaped, fashioned, treated, as if each were a kind of larger living room.

© Christopher Alexander and The Center for Environmental Structure