Complex Adaptive Cities

Complex adaptive systems are hard to understand. Messy and complicated, they cannot be broken down into smaller bits. It would be easier to ignore them, or simply leave them as mysteries. But given that we are living in one such system, it might be more useful to buckle down and sort it out. That way, we can make choices that are aligned with how the world actually operates.

In his book Diversity and Complexity, Scott E. Page explains, “Complexity can be loosely thought of as interesting structures and patterns that are not easily described or predicted. Systems that produce complexity consist of diverse rule-following entities whose behaviors are interdependent. Those entities interact over a contact structure or network. In addition, the entities often adapt.”

Understanding complexity is important, because sometimes things are not further reducible. While the premise of Occam’s Razor is that things should be made as simple as possible but not simpler, sometimes there are things that cannot be reduced. There is, in fact, an irreducible minimum. Certain things can be properly contemplated only in all their complicated, interconnected glory.

Take, for example, cities.

Cities cannot be created for success from the top down by the imposition of simple rules.

For those of us who live in cities, we all know what makes a particular neighborhood great. We can get what we need and have the interactions we want, and that’s ultimately because we feel safe there.

But how is this achieved? What magic combination of people and locations, uses and destinations, makes a vibrant, safe neighborhood? Is there a formula for, say, the ratio of houses to businesses, or of children to workers?

No. Cities are complex adaptive systems. They cannot be created for success from the top down by the imposition of simple rules.

In her seminal book The Death and Life of Great American Cities, Jane Jacobs approached the city as a complex adaptive system, turned city planning on its head, and likely saved many North American cities by taking them apart and showing that they cannot be reduced to a series of simple behavioral interactions.

Cities fall exactly into the definition of complexity given above by Page. They are full of rule-following humans, cars, and wildlife, the behaviors of which are interdependent on the other entities and respond to feedback.

These components of a city interact over multiple interfaces in a city network and will adapt easily, changing their behavior based on food availability, road closures, or perceived safety. But the city itself cannot be understood by looking at just one of these behaviors.

Jacobs starts with “the kind of problem which cities pose — a problem in handling organized complexity” — and a series of observations about that common, almost innocuous, part of all cities: the sidewalk.

What makes a particular neighborhood safe?

Jacobs argues that there is no one factor but rather a series of them. In order to understand how a city street can be safe, you must examine the full scope of interactions that occur on its sidewalk. “The trust of a city street is formed over time from many, many little public sidewalk contacts.” Nodding to people you know, noticing people you don’t. Recognizing which parent goes with which kid, or whose business seems to be thriving. People create safety.

Given that most of them are strangers to each other, how do they do this? How come these strangers are not all perceived as threats?

Safe streets are streets that are used by many different types of people throughout the 24-hour day. Children, workers, caregivers, tourists, diners — the more people who use the sidewalk, the more eyes that participate in the safety of the street.

Safety on city streets is “kept primarily by an intricate, almost unconscious, network of voluntary controls and standards among the people themselves, and enforced by the people themselves.” Essentially, we all contribute to safety because we all want safety. It increases our chances of survival.

Jacobs brings an amazing eye for observational detail in describing neighborhoods that work and those that don’t. In describing sidewalks, she explains that successful, safe neighborhoods are orderly. “But there is nothing simple about that order itself, or the bewildering number of components that go into it. Most of those components are specialized in one way or another. They unite in their joint effect upon the sidewalk, which is not specialized in the least. That is its strength.” For example, restaurant patrons, shopkeepers, loitering teenagers, etc. — some of whom belong to the area and some of whom are transient — all use the sidewalk and in doing so contribute to the interconnected and interdependent relationships that produce the perception of safety on that street. And real safety will follow perceived safety.

To get people participating in this unorganized street safety, you have to have streets that are desirable. “You can’t make people use streets they have no reason to use. You can’t make people watch streets they do not want to watch.” But Jacobs points out time and again that there is no predictable prescription for how to achieve this mixed use where people are unconsciously invested in the maintenance of safety.

This is where considering the city as a complex adaptive system is most useful.

Each individual component has a part to play, so a top-down imposition of theory that doesn’t allow for the unpredictable behavior of each individual is doomed to fail. “Orthodox planning is much imbued with puritanical and Utopian conceptions of how people should spend their free time, and in planning, these moralisms on people’s private lives are deeply confused with concepts about the workings of cities.” A large, diverse group of people is not going to conform to only one way of living. And it’s the diversity that offers the protection.

For example, a city planner might decide to not have bars in residential neighborhoods. The noise might keep people up, or there will be a negative moral impact on the children who are exposed to the behavior of loud, obnoxious drunks. But as Jacobs reveals, safe city areas can’t be built on the basis of this type of simplistic assumption.

By stretching the use of a street through as many hours of the day as possible, you might create a safer neighborhood. I say “might” because in this complex system, other factors might connect to manifest a different reality.

Planning that doesn’t respect the spectrum of diverse behavior and instead aims to insist on an ideal based on a few simple concepts will hinder the natural ability of a system to adapt.

As Scott Page explains, “Creating a complex system from scratch takes skill (or evolution). Therefore, when we see diverse complex systems in the real world, we should not assume that they’ve been assembled from whole cloth. Far more likely, they’ve been constructed bit by bit.”

Urban planning that doesn’t respect the spectrum of diverse behavior and instead aims to insist on an ideal based on a few simple concepts (fresh air, more public space, large private space) will hinder the natural ability of a city system to adapt in a way that suits the residents. And it is this ability to adapt that is the cornerstone requirement of this type of complex system. Inhibit the adaptive property and you all but ensure the collapse of the system.

As Jacobs articulates:

Under the seeming disorder of the old city, wherever the old city is working successfully, is a marvelous order for maintaining the safety of the streets and the freedom of the city. It is a complex order. Its essence is intricacy of sidewalk use, bringing with it a constant succession of eyes. This order is all composed of movement and change, and although it is life, not art, we may fancifully call it the art form of the city and liken it to the dance — … to an intricate ballet in which the individual dancers and ensembles all have distinctive parts which miraculously reinforce each other and compose an orderly whole. The ballet of the good city sidewalk never repeats itself from place to place, and in any one place is always replete with new improvisations.

This is the essence of complexity. As Scott Page argues, “Adaptation occurs at the level of individuals or of types. The system itself doesn’t adapt. The parts do; they alter their behaviors leading to system level adaptation.”

Jacobs maintains that “the sight of people attracts still other people.” We feel more secure when we know there are multiple eyes on us, eyes that are concerned only with the immediate function that might affect them and are not therefore invasive.

Our complex behavior as individuals in cities, interacting with various components in any given day, is multiplied by everyone, so a city that produces a safe environment seems to be almost miraculous. But ultimately our behavior is governed by certain rules — not rules that are imposed by theory or external forces, but rules that we all feel are critical to our well-being and success in our city.

Thus, the workings of a desirable city are produced by a multitude of small interactions that have evolved and adapted as they have promoted the existence of the things that most support the desires of individuals.

“The look of things and the way they work are inextricably bound together, and in no place more so than cities,” claims Jacobs. Use is not independent of form. That is why we must understand the system as a whole. No matter how many components and unpredictable potential interactions there are, they are all part of what makes the city function.

As Jacobs concludes, “There is no use wishing it were a simpler problem, because in real life it is not a simpler problem. No matter what you try to do to it, a city park behaves like a problem in organized complexity, and that is what it is. The same is true of all other parts or features of cities. Although the inter-relations of their many factors are complex, there is nothing accidental or irrational about the ways in which these factors affect each other.”