Tag Archives: city networks

A conversation about the geometry of nowhere

In response to my last article, Bruce Liedstrand of Community Design Strategies in Paris writes,

I read with interest your essay on The Geometry of Nowhere because I divide my time between Paris and Silicon Valley (the site of your Cupertino Target store example). After re-reading the essay, I am puzzled. I hear your frustration with narrow sidewalks, but I am lost in understanding your concept of “place”.

My experience has been that a “place” is created by spatial enclosure, the use of adjacent buildings to enclose and shape the space into a comfortable “place”.  Paris is strong on spatial enclosure. To me it seems almost as if Paris started as a solid mass and that the boulevards were carved out of the mass by broad blades and the narrower streets (“rues”) by finer blades. Wherever I am in Paris I feel comfortably inside a good place.

Your essay seems to indicate that “place” exists without any enclosure by buildings. That, indeed, it can exist on the outside edge of buildings rather than inside a group of buildings. Is that what you intend?

I am puzzled also by your discussion of the Cupertino Target store, which I have personally visited. (Ed note: What are the odds?) When I look at your illustration of your changes, I don’t see any “place”. What I see new is open spaces outside buildings from which cars have apparently been excluded. Do you intend to say that exclusion of cars is the key to converting undifferentiated open space into a good “place”? What is it about these new open spaces around the store that would make them comfortable for people to linger in?

Perhaps I am reading your essay wrong? Can you please point me in the right direction?

Thanks.

Enclosure creates a room, but it’s not sufficient to create a place. You can see this in Paris, where some of the best places in the city are not enclosed, for example along the Seine, or the Luxembourg garden. And the most enclosed places, like Place Vendôme, are not very interesting.

To get a good understanding of the relative impact of enclosure and open space on place, all we have to do is take a long walk along the axe historique. Start at Place de la Concorde, which was about 50% sidewalk 50% free space when it was created and is not enclosed. All the free space was converted to road and now it is perilous to get across, but still a place. Walk down to Rond-Point de l’Élysée through a wood with substantial open space to walk across. I don’t know if that counts as enclosure, but it’s a good place. Then you have the model of place, the Avenue des Champs-Élysées with its straight-aligned buildings, that is also a place with 50% sidewalk and 50% road. And it is a major road, 10 lanes of traffic, but that doesn’t really interfere with it as a place because there is little reason to cross the road, and it can be done in two steps thanks to traffic islands.

Once you’re up the hill and you go across the monster Place de l’Étoile (horrible place, all cars driving maniacally so that pedestrians have to cross in underground passages), you end up on Avenue de la Grande Armée, which is morphologically identical to the previous avenue except that some of its space is taken by parking lots. That means the ratio of sidewalk to road is much less than 50/50. It’s also much less crowded and much less attractive than the previous avenue, but it still works.

After you get across Porte Maillot to Avenue Charles de Gaulle in Neuilly, then you find the same buildings with the same alignments and the same enclosure as the two previous avenues, except this time the space has been traffic-engineered to hell, combined with speed cameras to dissuade speeding. What space there was on Grande Armée has been cut even further, and the result is a dead street on what is a major business center of the city.

Finally cross the bridge and climb your way up to the Parvis de La Défense, where you will find that the buildings are modern and completely random, but the space is fully open to people and always full of people. (Even on Sundays!) I interviewed the master planner for the northern expansion, and he said the developer of La Défense did not agree to build the 25m wide pedestrian bridge he had designed to connect the site to the main place. After their small “passerelle” failed they backed down and built the full bridge, and it works, always full of people.

So there you have it, the closest thing to a controlled experiment on place and enclosure. Enclosure turns out to be irrelevant.

Have a nice walk.

Do you really find La Defense a pleasant place?  For me, it is utterly placeless – one of the worst locations in Paris?

If you have extra time on a pleasant afternoon, would you really rather spend it sitting in the open space of La Defense than in my neighborhood park?

p1010675_4

La Défense is a business place, and it works at what it is. But compared to Avenue Charles de Gaulle, which is another business place, and which has the same architecture and alignments as the rest of Paris, it is a much better place.

Can you say this is not a good place?

Look at all the people. They’re not locked up in their offices. The neighborhood is set up so you can go straight to your office to the metro using tunnels, but when I was there I always preferred taking a detour on the surface. Take my word for it, people even go there on the weekends to teach their kids how to ride bikes and roller-skate. They don’t care that the buildings aren’t aligned.

What I am asking with my article is how can we reduce and remove sprawl without going through an expensive process of total demolition for which we won’t have the money anymore? We don’t have the choice of your small neighborhood park. A place and a park are very different things anyway. Cities existed for centuries without parks, but never without place. If we reintroduce place in sprawl cities, that means shops that rely on place to survive don’t have to open up in the mall anymore, they can do business anywhere because the entire city is a mall (one of the first things I realized about Paris). Then your city starts to grow around place instead of around roads, and people have a reason to linger.

Yes, for me it is not at all a good place in the photo or in personal experience.  People are dwarfed by the size of the space (in the photo, the space is almost empty) and it is not comfortable.  One can look at the buildings as perhaps interesting objects, depending on one’s taste, but it certainly is not a place I would linger in or return to regularly if I didn’t work there.Let’s accept that we disagree, vigorously, about whether La Defense is a good place.  But what, in your view, makes a good place.  So far I hear you favor an absence of cars and openness?  Is that right?  Is that all, or can you tell me more?

And what would be good about your redesigned Target store?

I didn’t redesign the Target store, I left it there as a necessity of the context, and the people at La Défense aren’t looking at the buildings. They’re a necessary part of the décor, but they’re not the reason people use the place, or any place.La Défense became a success, despite everyone’s intent, because economic conditions forced the developers to break the master plan and allow any random building to be built. Had they not done so it would be exactly like Empire State Plaza in Albany. The difference between the two is not architectural, it is socio-economic.

You do not need to remove cars to make a good place, you only need to remove the exclusivity for cars. What makes a good place is total freedom of movement for everyone, including the freedom to stop and linger. You can’t do that in traffic engineered space because you are confined between very narrow limits. They tell you how fast to go, when to stop, where to turn, it’s a nightmare, but one that we put up with to go fast.

Is an empty space out in the desert a good place because everyone can move freely?  Or are you talking about places within cities?  Is it just traffic engineered spaces that you reject?  Are you advocating a Hans Monderman approach to streets?  Are you rebelling against “confinement”, or is some broader principle involved?

I agree that the Empire State Plaza in Albany is a terrible place.  Are you saying that the only problem with it is that, unlike La Defense, the buildings are not place at random?  What do you mean by saying that the difference is “social-economic”?

Could you please write in one paragraph what you believe are the key factors in creating a good place within a city so I can understand where we might agree or disagree?

Deserts can make a good place, although there is not much desert urbanization. (Desert driving is a lot of fun nevertheless.) Open space alone does not make a place, you also need people there, and the reason that people go through any place is to participate in and generate social and economic networks. This was not done at Empire State Plaza but was done at La Défense.

The issue is at core about freedom. How much freedom of movement do I enjoy, how much freedom to grow and build do I enjoy? In a place you can walk anywhere and build anything anywhere, or just occupy the space to conduct some activity like playing hockey or learning to ride a bike. That creates networks and attracts people. In sprawl the entire space is traffic engineered. To move around you are practically on a conveyor belt, offered only a linear path, delimited speed and a select few choices. You can’t build anything because of the zoning. The choices available to you have been selected by the traffic engineers and the planners, and they only fit  their model of what they want you to do. There is no creativity possible to invent your own journey. A famous game designer once said “a game is a series of interesting choices.” What kind of choices does sprawl offer?

The one place in sprawl where people are given a shred of creativity is the mall, and that’s how people who live in sprawl spend their free time. You can go there and just hang out, inventing an activity from nothing. It’s all the place they have left.

The complex grid

In a medieval-era city the pace of urban growth is slow to a point where the growth of the city is not consciously noticed. Buildings are added sporadically, in random shape and order, as the extremely scarce economic situation makes no other pattern possible. Typically this means that the shape of streets will match the existing natural paths of movement, giving the street network an organic structure that is preserved through successive transformations in the urban fabric.

This works until the street network becomes large enough to become a functional problem. Because it is random, the medieval street network becomes complicated to move around in once the structure exceeds a certain scale. Some people see this as an obstacle to commerce and project to restructure the emergent medieval grid into something more rational. These projects fail for the same economic reasons that shaped the emergence of the medieval streets.

As the pace of urban growth increases and as the cartesian paradigm expands in the 17th and 18th centuries, deliberate city planning through the pre-emptive definition of an urban grid becomes fashionable. The practice of baroque planning remains the privilege of ultra-rich landlords considering the scale of construction involved. (Louis XIV’s Versailles is still the case study.) In the Americas such concentrations of capital do not yet exist. Grids are not truly part of a city plan, they are the outcome of regulations meant to avoid the pitfalls of medieval urban growth. Although the idea of a block is defined, the limiting shape of the grid itself is undefined. This allows cities to grow out, in theory, infinitely.

This works until the grid encounters and existing structure in the landscape. While Europe’s land is already very complex, in America the land is mostly empty. One exception is New York, which has multiple grids expanding towards the center of Manhattan, all with their own alignment with the waterfront. Compounding the medieval streets below Wall Street, the city’s network is getting messy. The solution conceived is the first city plan of New York, the Commissioners’ Plan of 1811, which grids Manhattan in the pattern it is famous for to this day with the help of a concentrated political power. In Europe this much centralization is not available, cities being ringed by a large number of villages that already structure the land. One notable exception is Barcelona, which under conservative military domination had reserved a large non aedificandi zone outside of its defensive walls. With the military out of the picture, and the industrial revolution putting enormous pressure on the city’s growth, the next most famous cartesian grid plan is imposed: the eixample. Adepts of the medieval city such as Camillo Sitte praise its artistic value and quality of life, but fail to truly describe how to reproduce it in the context of accelerating urbanization.

The 19th century is the triumph of the cartesian plan. It is not only employed to plan cities but to plan the entire American landscape. West of the original colonies the map becomes rectilinear. The flexibility and fluidity of New York’s grid plan promotes very rapid land development and the city achieves growth rates never before seen. European city planners are facing the same growth pressure but are trapped by the land’s existing structure, both physical and political. One simple solution is discovered: demolishing city walls and building a high capacity road that encircles the city, the boulevard. If it is to be complicated to get inside a city, it will at least be simple to get around it. Paris builds two on its two successive walls, and Vienna builds the famous Ringstrasse. An interesting phenomenon emerges from subsequent growth. While the boulevards were meant to be restful promenades, they emerge to become important centers on their own due to their attractiveness for traffic. In space syntax terms, they are integrators.

Manhattan’s grid extends to over a hundred streets but starts to suffer from severe scale problems. The medieval street system drives traffic away to boulevards, but in an endless grid traffic goes everywhere, and there is no place that is free of the increasing congestion. With the introduction of the car the endless grid is in crisis. Since no better idea is found, the grid system is replaced with the high-capacity collector road to concentrate all the congestion, from which huge, isolated developments  access each other. This is the suburban sprawl system that remains the norm. It has the advantages of being simple to plan and giving enormous clout to land developers. However people are dissatisfied with the enormous scale of their environment. That they enjoy a single-family home does not sufficiently conceal the fact that they are clustered with thousands of similar homes, and next to those are huge strip malls, office parks and shopping malls that require long vehicle trips to access. The disconnect between their homes and their activities means they live in a form of crowded isolation. The suburbanites escaped congestion only to arrive at emptiness. There is more life in the less populated countryside. Adepts of the metropolitan grid such as Rem Koolhaas praise the culture of congestion as a lifestyle that the collector road fails to create.

This was as briefly stated as I could the modern history of the urban network: one system failing to adapt to the scale of the city, being replaced by a larger system that erases the small scale complexity of the previous only to itself fail at a much larger scale, and then another larger system crushing all complexity to resolve a problem of modernity.

Is there a way that we could have the benefits of all systems balanced as a whole urban network? To describe such a system, we can first define some proscriptions.

  • Any size of urban growth is allowed as long as the new growth extends the boundary of the network. This ensures that the city has the economic flexibility of the medieval city and allows anyone, no matter their economic importance, to contribute to the city’s growth.
  • The network must not become so complicated that it becomes impossible to move around in order to participate in large-scale activities and a culture of congestion.
  • Streets must not grow too long without interruption in such a way that speeding and traffic accidents are encouraged.

How does this work out in terms of prescriptions? It turns out to be very simple. If we assume that we start with a hamlet of a single block, or a regional road that is undeveloped, we need only two rules: one for private development and one for the community.

  • For private development: you may build on any available part of the network so long as you replace the part you used up by extending the network around your new block.
  • For community development: any time a part of the network becomes too complicated (for example it takes more than 4 steps to get out of a sector), extend the boundary of that part with a higher capacity road (a boulevard).

How do we tell if these two rules really do meet the proscriptions we defined? Since we’re talking about an emergent design, the only way to see how it works is to do an explicit simulation of the computations involved. For this I employed a Fibonacci sequence to stand for a random growth process. With each new block that the sequence generated, I placed it in the section of the network that minimized the private cost of extending the boundary. I also used square blocks to simplify the computations involved, and also to demonstrate how such a process would work in a structure of land that has been made square, for better of worse, through cartesian planning. The process would work just as well in a more fluid, rounder land structure such as exists in Europe and the American East.

Stage 1: The village

complex-grid-village

The village is a cluster of houses and small businesses, whose only real challenge is maintaining a facade with the outside by ensuring that every new block also fronts the countryside. This provides the village with a path that everyone can walk around on whenever they want to get some fresh air and open space.

Stage 2: The town

complex-grid-town

The town starts to support development at larger scales with bigger block sizes. The first boulevards are built around the original village, preserving its traditional atmosphere from the growing businesses on the new boulevards.

Stage 3: The city

complex-grid-city

Now a significant regional center, the city’s economic complexity is heralded by the construction of the ring road enclosing the town’s neighborhoods. Large developments such as a regional shopping mall, an airport and a TND line the ring road alongside other smaller blocks of more traditional housing and business that take advantage of the high centrality of the ring and its new culture of congestion, eventually forming whole neighborhoods of their own. The ring road also encloses available green spaces for recreation, making it a parkway in some segments.

Emergent properties of the process

The most interesting outcome is that the structure of the network makes a very nice chaotic fractal, showing the balance between scales in the city’s growth. It is simultaneously simple to grasp and complex, living geometry.

complex-grid-fractal

The spatial integration created by the boulevards and ring roads also promotes the creation of a hierarchy of different centers that are evenly distributed between neighborhoods. Tightly knit residential quarters provide security for children and the elderly, with neighborhood centers within walking distance and no threat of heavy traffic until the edge of the city, liberating citizens from automobile dependency.

Adopting a complex grid is going to benefit small towns and villages most, as their economy is typically not large enough to support the collector road system. It might even result in the emergence of new villages in rural regions that have experienced large-scale urbanization and thus make them more resilient to economic shocks.

For existing cities, history provides a precedent for increasing the grid’s complexity when the problem is scaling up the grid. The urban renovations of Haussmann in Paris or Robert Moses in New York showed how to compose a larger scale within an existing city. (In Moses’ case, how not to do so as well.) However there is no precedent for scaling down a network that is too big, which is what modern cities suffer from. I suspect that contrary to scaling up which requires a strong centralization of power, scaling down involves a decentralization and a multiplicity of new powers transforming neighborhoods, breaking up regional, municipal and even neighborhood authorities such as homeowners’ associations to create local economies.

Scale-free urban systems

In previous comments, I have argued that what makes cities different than building projects was the fact that they have to deal with change and uncertainty, and that subdivision-planned developments are economically inferior to random growth. These arguments rely on the fundamental quality of cities as systems, a property that places them in the same class as biological systems while separating them from mechanical systems. This quality is being scale-free. That is to say, a city can work no matter what size it takes.

The ability of a system to function at multiple scales is behind the growth process of all multicellular lifeforms. It all starts as a single embryo, multiplying into thousands and millions and billions of cells. These cells work together to emerge the form of a sapling, which immediately begins to function autonomously as it grows into a full-sized tree. The processes in the DNA of a tree are able to function at whatever scale the tree grows. They can work even if half the branches are cut off, for example to make one of those distinctively-French square trees.

It should be obvious that this is a radically different quality than those possessed by mechanical system. We cannot imagine a car growing with us over the years. We cannot imagine a car working if one of the wheels is taken away. In a mechanical system, action is linear. If one system or sub-system fails, the whole structure fails. In a scale-free system, no single sub-system is that critical, although they each have a marginal impact on the total efficiency of the structure. So a tree might not die from being cut square, but it will not function as efficiently.

The idea of creating something whose size is not going to be known is alien to engineering and architectural practices. But this is not to say that it has never been done before. The Internet is without a doubt a great achievement of scale-free system design. Its foundations, Arpanet, was intended by the military men to be a communications system that could function through a nuclear war, which implied a catastrophic loss of infrastructure in random places. The cables and links that you are using relate directly back to this original system, and they have grown to such a scale that no one really knows how big it is. If it works, don’t fix it. But how does it work?

The idea of a network that could continue to function despite bombardment was actually demonstrated in World War II, when large-scale strategic bombings of cities devastated Germany and Japan. Quite surprising was the fact that, instead of resulting in a massive exodus of urban populations to the countryside, leaving ghost towns behind, bombed cities continued to function, supporting the lives of their residents and industrial war effort, although with greater hardship. Despite catastrophic reduction in scale, cities adapted and continued to work. The modernist plans for cities of 1,000,000 people of the time were set up to fail. By designing in advance the final form of a city as if it were a building project, just bigger, modernists failed to understand the fundamental benefits of cities. Even those plans that were realized, like Brasilia, face intense pressure to change their scale and grow new relationships, as witnessed by Mr. Bill Hillier.

The systems that allow the internet to work are founded upon relational rules. It is by defining protocols for how different networks relate to one another that all of them come together to form the Internet, without any of them being really aware of the scope of the entire system. The form the system takes is fractal. (A fractal is a relational rule applied repeatedly.)

The most simple form a city can take is that of a village on a road. But what is the difference between one village in the countryside, and 100,000 villages in a metropolis? It is the spaces that tie them together at a larger scale. From an “urban village” where your house is you enter an avenue, which has shops and activities and businesses along with faster movement. The avenue relates the villages together, and the grand avenues relate the avenues together. The expressways link the grand avenues, all the way up to the airports who link the cities together. Building these relationships is the basic day-to-day work of city corporations.

Relational rules also appear in the essential tool of urban planning, the building code. Building codes ideally allow the maximum flexibility in local problem-solving, the design of a building, while integrating the building smartly into the urban fabric of the city as a whole. A good building code is itself scale-free. It defines how anything from a bungalow to a soaring skyscraper is to be shaped in order to be compatible with the whole.

If done right, a city plan will work beautifully whether it is growing or shrinking, whether it has ten inhabitants or ten million. The job of designing cities is not so much about determining form, but about defining the processes that will generate their form.