One of the biggest problems confronting today's cities—and underlying arguments about transport, house prices, schools, and hospitals—is their sheer size.
A century ago, only 1 in 10 people worldwide lived in cities; today it is more than half. And as the human race becomes for the first time in its history a predominantly urban species, city planners face the question of how to arrange all these residents so that they can get around, afford homes, see doctors, and get their children educated. And not just that, but they have to figure out how to do it while emitting less carbon and spending less money.
One solution that lots of places are working on is to raise their city's density, the number of people in a given amount of space. The logic is that if you let your city sprawl ever further outward into lots of low-density suburbs, like in Los Angeles, it's expensive and carbon-intense to build a network of transport and services; a problem compounded by the fact that the amount of tax you're taking in per square foot goes down.
As the city gets denser, on the other hand, more people are within easy reach of every school or bus stop. There's no better visualization of this than a metro map. In a city center, the stations are thickly clustered, each a short walk from the next, while at the outskirts you have long, thin arms floating ever further away from one another.
To raise density and pack more people into the space, cities as varied as Toronto and Kigali have recently passed laws against sprawl, forcing the city to grow upward rather than outward. But Medellin, in Colombia, where the population tripled between 1951 and 1973, and has since almost tripled again to reach 2.4 million, has come up with something cleverer. To put a hard stop to outward expansion, a place once notorious for its drugs and gang warfare is laying out a circular garden around the city limits. Employing 5,000 people for 15 years, the garden is to be 46 miles in circumference and will also address one of the complications for a very dense city: the potential lack of green space.
Many of the best attempts at increasing density take into account the growing need to overcome lack of green space, leading to a global surge in futuristic "vertical parks." The most famous example, the Bosco Verticale, opened in Milan in 2014. A pair of tower blocks 27 stories high, the vertical forest has a total of 900 trees all the way up every side, filtering pollution, absorbing water, and mitigating the urban heat trap.
Meanwhile Paris is building a thousand-tree park and housing development on top of a section of the city's ring road. Designed to act as a bridge over the highway, it is also intended to get more people into the available space without creating a concrete termite mound.
Another crucial complication is of course the rising cost of space. There are various ways to get around that, the most obvious being to build apartments rather than row houses. London, the world's most expensive city by property prices, is girdled by a broad swathe of space-inefficient terraces, stretching 20 miles from one end to the other. During the last phase of transformative urban renewal, in the 1960s, half a million terraced houses in Britain were demolished to make way for flats.
Another obvious measure is to make sure every available inch is actually being used. Saudi Arabia has just broken with its anti-tax traditions to impose a charge on any unoccupied urban space, while Paris has passed a law quintupling its tax on unoccupied homes.
But as well as creating complications, making a city denser allows you to do things you couldn't do before. So Barcelona is using its density to reclaim 60% of its streets from the noise and pollution of the car. Groups of nine city blocks are being amalgamated into super-blocks that allow cars only on their perimeter. Inside each super-block, cars are permitted only for residents or deliveries and are limited to a top speed of 10 mph.
The German city of Mannheim is going even further, laying out a neighborhood to have no cars at all. In fact, this neighborhood has no roads. The (affordable) houses are interlinked by treelined pathways and fruit gardens that encourage residents to come out of their houses and into the public space. Connection to the rest of the city is provided by the main road that runs along the edge of the neighborhood, and by a tram stop.
This is the future that density promises: One that is clean and quiet, where children can play in the streets, where everyone's health improves because they aren't breathing in smog, and where you only need a car if you're going away for the weekend.
Of course that only works if you build the right infrastructure. Many of Asia's megacities are already far denser than Western equivalents; there are four times as many people for every square foot of Seoul, for example, as for Berlin. And surely no one would consider Mumbai an urban utopia.
Some people might also say that they don't want to live in an apartment; they want to live in a house. I'm one of them. But if cities are to be sustainable as they grow, the most important reason for embracing density is perhaps a change of mind-set. The suburban house—and the car needed to reach it—symbolizes a kind of individualism that just doesn't work when there are tens of millions of us trying to all be individuals in the same place.
It also fits into a simplistic myth of how life is actually lived, one especially propagated by the suburb builders and car salesmen of 1950s America: that each of us determines by his own desires and talents where and how fast he travels. There is no simpler demonstration that that is nonsense than a traffic jam.
Those of us living in cities—which is now most of us—all live together, for better or worse. We can either accept it and embrace the best of what density offers, or spend our lives bumper to bumper on the motorway, each in his own pod, cursing everyone else.
Alexander Starritt is the editor of Apolitical.
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