We've spoken before about Saudi Arabia's "The Line" project. At first, I wasn't sure if it was real, but it is, and it's now under construction. We then spoke about whether a 170-kilometer line is an optimal urban form for a city, and the answer, according to this study, is that it's not. The problem with a line is that it actually maximizes the average distance between inhabitants. This makes sense because you could have two people living and working 170 kilometers apart.
On the other hand, if you maintain the same built-up area and take the opposite kind of geometry -- a circle -- you actually minimize the average distance between inhabitants. It's for this reason that older cities (the ones that weren't masterplanned) have tended to grow radially and not linearly (unless there were geographic features forcing it to grow in a certain way). So there is a strong argument to be made that The Line is a suboptimal plan for a new city.
But here's what's interesting: many cities already follow a somewhat similar approach. They don't do it as absolutely as The Line, but they do it in the way that they zone for higher densities and a mix of uses only on their main corridors. Example:
So I guess I was wrong. I thought "The Line" in Saudia Arabia was never going to be built -- at least not in its current incarnation. But apparently it is now under construction, and it is still planned to be 170 km long and house some 9 million people when it's complete. I suppose something could happen between now and when all 170 km are complete, but I'm happy to accept that, for the time being, I was wrong.
Now it's time to ask ourselves what a 170 km long city would even be like. To answer that, here is a fascinating article from npc Urban Sustainability describing how mobility and urban interactions are likely to work in this kind of a linear city. And it turns out that a line is actually an optimal urban form if you're trying to both maximize commute times and maximize the average distance between inhabitants:
One of the most critical aspects related to The Line is distance. If its 9 million inhabitants are homogeneously distributed in the city, each km will have roughly 53,000 people. If we randomly pick two people from the city, they will be, on average, 57 km apart. Although The Line occupies only 2% of the surface of Johannesburg, if we pick two random people in Johannesburg, they are only 33 km apart.
In this recent post by Naval Ravikant, he argues that innovation seems to like two things: decentralization and a frontier. He starts by giving the examples of more decentralized states (i.e. smaller federal governments) and the Wild West. The American frontier was, as you know, wild. But it was also a place of great innovation.
Naval then goes on to talk about the pendulum that tends to swing between centralization and decentralization. And in the world of technology, the last decade has been one of centralization (big companies). But this pendulum is much broader. Cities, as we have talked about before on this blog, are constantly in tension between centralizing and decentralizing forces.
COVID was a powerful decentralizing force for cities. Everything was closed and we were all supposed to stay home. And so most/all of the benefits of centralizing in a city were suddenly, yet temporarily, turned off. Many people naturally decentralized. But when the dust finally settles, I highly doubt it will be as dramatic as most people initially thought.
This creates a similar kind of effect when it comes to walkability, ability to support higher-order transit, and overall agglomeration economies. All of the urban activity gets concentrated along one corridor, maximizing the distance between people. In extreme examples, you also get inhabitants that are forced into different mobility options. The corridor is supposed to be transit-oriented, but all of the surrounding areas are really only conducive to driving. This creates a mismatch that is less an ideal for everyone.
So this post is our regular reminder that, when it comes to planning cities and bringing people together, circles tend to be better than lines. This doesn't necessarily mean that you need to adopt some sort of radial street network, à la French model. (Although I'm now thinking about the effects of this vs. an orthogonal grid.) It just means that urban density works a lot better when it's clustered, especially around transit. And generally, circles make for better clusters.
Keeping the surface fixed, a line is the contiguous urban form that maximises the distance between its inhabitants.
In The Line, people are as far away from others as possible. Considering that a walkable distance is 1.0 km, in The Line, only 1.2% of the population is at walking distance from others. Active mobility is not viable in The Line since distances are too long. The plan for The Line has no cars but also gets rid of most active mobility. Although in The Line, basic needs could be satisfied within 5 min, most journeys to school, work, leisure or visiting other people will depend on public transport.
So what would be better? Well if you're trying to minimize the average distance between people and increase urban interactions, then the optimal form is generally the one that cities have been using ever since they were first created:
We can think of a city called The Circle, where we take the same tall buildings as in The Line but put them next to each other, forming a circular shape. A circle that occupies the same surface as The Line (34 km2) has a radius of only 3.3 km. In The Circle, the expected distance between two random people is only 2.9 km. In The Circle, a person is at a walking distance of 24% of the population (and within 2 km, they could reach 66% of the destinations), so most of their mobility could be active. In The Circle, a high-speed rail system is unnecessary since people could walk or cycle to most places, and buses could supply the rest of the journeys. The Circle occupies roughly the same surface as Pisa, Italy, but has 50 times its population. A round urban form is the most desirable since it reduces commuting distances and the energy required for transport.
This is one of the challenges with building large scale cities from scratch. It's easy to become enamoured with a particular plan or symbol; whereas in reality, cities don't care about these kinds of visual representations. They don't care that, in plan, the city may look like an eagle (see "Helicopter Urbanism", a term that was supposedly coined by Jan Gehl). What matters is how interactions between humans play out at street level.
"unicorns" tend to overwhelmingly originate in big cities
. But here's the thing: this is a form of centralization. The fact that cities even exist in the first place tells us that their centralizing forces are winning out over the decentralizing ones.
So how do we reconcile this with Naval's argument that new frontiers and decentralization are actually what are needed for innovation? I agree wholeheartedly that one of the key innovations with crypto, for example, is that it is decentralized and permissionless. But what does this ultimately mean for cities and our built form?
Does it encourage a similar sort of decentralization to happen? Or is the irony that decentralized technologies actually still thrive in centralized urban places? We may all be online buying NFTs, but we still want to get together in person to show them off and exchange ideas.
