And my memory immediately took me to a conversation with colleagues about how a suburban lifestyle could be adapted to fit a dense urban context.
To bring you up to speed: We were designing a luxury high-rise building in a downtown zone within an otherwise car-centric, super sprawled city.
For this to be successful, we needed to create an offering so compelling that it could compete with the suburban market. This is hard, because the greatest asset of a suburban home is spaciousness and privacy. Both are possible in dense urban environments, but they look very different.
How do we create spacious living areas that can easily entertain dozens of guests? What does decent replacements for backyard BBQs look like? How about the privacy of hedges and fences on balconies? Where can the kids run freely in a closed environment that parents can supervise 100%? Does each unit get a wine fridge?
We came up with a hybrid of amenities sold as superior environments over their suburban counterparts. Large private terraces and even larger building amenities had everything a small neighbourhood park would have and more. Generous dining rooms with bars and kitchens, in-house libraries and studies… a number of ideas flowed out during a design session.
While the design issues were one thing, something else felt odd at a different level.
We were equipping a condo with enough amenities for a neighbourhood, and no one except the residents of this building could benefit from it.
The prospect of a suburban lifestyle in an urban context was playing out right in front of my eyes, and I didn’t know how to feel about this.
Fortunately, Christopher Alexander (who I’ve written about in the past) had a way to articulate that which I was unable to back then. We must look at one of his very first essay that he ever wrote on his thoughts: The City Is Not A Tree (1965).
I am aware that his ideas were just starting to take form back in 1965. He would be more than a decade away from writing A Pattern Language, published in 1977. However, the structural seeds in this early essay contain useful ideas to begin grasping what was going on.
Why does he say that “A City Is Not A Tree”?
A tree, in common parlance, consists of a trunk with branches, and those branches have more branches until you find yourself at the tip of a new branch.
I can hear you all: “Yes, Fei, we all know what a tree is, gosh”
But herein lies the kicker: at no point do two separate branches ever merge and meet downstream of a split. Every branch is isolated from other peer branches.
This trait is what makes a tree a tree in the Alexandrian sense.
The tree structure is essentially how we prefer to talk about our ownership structures. Clear-cut lines are the easiest to handle. This is my area, that is your area, and that over there is the public area.

Cities, in his mind, are not meant to be thought of as a tree, or simply hierarchical parts of a whole. You want things to collide, intersect, and interact at the branch level to form new synergies, or new “wholes” as he much later would come to describe these phenomena.
The difference can be visualized too. Look at the left-hand graphic first for the tree-structure, and then at the right-hand graphic for what he believed a city was more like:

Alexander described the attribute as a “semi-lattice”.
I think of it as interdependence.
Interdependence forces us to have to consider others in our space. We become softer in our boundaries. As a result, we must care what others think because it’s not just us living there. Sharing leads to caring.

What often goes terribly wrong in living conditions like this is that we go into them with the TREE mentality. We want independence. We want to just deal with our own crap, and not other people’s crap. We carry a less compassionate frame of mind.
The problem is, this is very brittle and fragile behaviour. What if something happens to you? Who will know? What if one critical branch breaks? The whole downstream section that relies on that branch will be affected. Suburban road structures are terrible at handling load for this reason. There is no redundancy and overlap in service. Strong Towns calls this “complicated” behaviour.
The way we were designing the luxury condo above was based on a philosophy of a tree structure. There was very limited overlap in ownership. The building becomes a bastion within a neighbourhood.
Can we design high-rise buildings with more overlap and shared ownership of spaces? Maybe.
But what is stopping us is structures of ownership, and how transactions, insurance, responsibilities etc are outlined in law.
Drawing hard lines on a map is infinitely easier to manage than a negotiated, fuzzy boundary defined by a messy dialog between two or more people.
However, it is within these messy dialogs that interdependent relationships emerge, and the beauty of urban dreams truly shine.
As we shape our tools, our tools shape us in return. We are building our communities like trees, filled with pockets of isolation.
Let’s talk about that.