The Global Urbanist

News and analysis of cities around the world

The four keys to urban expansion identified at the World Urban Forum

At the World Urban Forum in Naples last week, both global urban policy and quantitative research efforts converged on a single conclusion: that the spatial planning of massive new urban expansion areas surrounding their cities is one of the most important things any government can do to make urbanisation sustainable.

Kerwin Datu

Kerwin Datu

Cities: New York-Newark, Paris, London

Topics: Integrated planning, Land, Housing, The global urban agenda

Some 8,000 registered participants and 16,000 exhibition visitors made their way to the World Urban Forum 6 in Naples last week, the flagship biennial event organised by UN-HABITAT. Round tables of ministers, mayors, parliamentarians and other leaders were convened, hundreds of discussions on everything from accelerating housing supply to slowing down cities were hosted, and thousands of chance encounters ensured an impossibly busy week for everyone. Much of the material presented was naturally very self-promotional, but a few strands of discussion stood out for us that we will share over the course of the week.

For example, after a hesitant first few months on the job, the UN-HABITAT Executive Director Joan Clos has now regained his clarity on urban growth. 'There is no development without urbanisation,' he now declares confidently, preaching very much to the unconverted mayors of the world who still believe urban population growth can be suppressed simply by refusing to plan for it.

'If expansion is not planned, well, it's going to happen anyway. And if it's not planned, then it's unplanned,' — a tautology with a serious point to make, which is — 'and the standard mode of unplanned expansion throughout human history is the slum.' With the world's urban population expected to grow by over 2.5 billion before what Schlomo Angel calls the world's 'urban project' is completed, that is a lot of potentially unplanned growth if politicians do not start taking urbanisation seriously. And with over 90% of this expected to occur in developing countries, the burden falls overwhelmingly on governments with little resources to manage it.

For leaders of these cities, Clos has another simple message: if you can't afford to build the infrastructure, at least plan the rights-of-way across the land where new areas can be expected to emerge. Buying this land, or legislating for its future acquisition, before its prices shoot up due to speculation, is one of the most cost-effective ways for poorer cities to plan now for their long-term expansion.

The reality of falling densities

Later in the week, the urban planning professor Shlomo Angel presented an extremely important body of research completed under the aegis of the Lincoln Institute of Land Policy, the eminent American research centre concerned with land use issues around the world. Using two samples — 120 cities from 1990 to 2000, and 30 cities from 1800 to 2000 — Angel and his team began by precisely mapping their expansion at specific intervals over time. This is the kind of exercise that has been undertaken hundreds of times before; what is significant in this study is how together these maps demonstrated surprising patterns about urban expansion and density.

One of the most significant findings is that cities almost always become less dense as they expand. 'I have not found cities densifying anywhere, except for Singapore,' which as a small island nation has natural limits on its horizontal expansion.

What this means is that as a city's population grows, the land it uses up does not simply grow — it accelerates. And, like cumulative interest rates on a bank account, the effect can be dramatic. For example, while over the 200-year period sampled Paris' population grew 16 times from 581,000 to over 9.5 million, its land area grew over 150 times from 1,170 hectares to nearly 180,000 hectares.

Echoing Clos' admonitions, this land use growth can be planned or unplanned, and both have their historical precedents. Angel refers to Queen Elizabeth I's proclamation that no structures should be built more than three miles outside the walls of the City of London, a policy as short-lived as it was short-sighted. By contrast, at a time that the built area of New York City occupied little more than the southern tip of Manhattan, its leaders instituted the grid that now covers the entire island, planning ahead for a sevenfold expansion of the built area. When the grid was filled up, they planned another sevenfold expansion effected with the incorporation of Kings, Queens, Bronx and Richmond Counties as boroughs of the city.

Four policy keys for urban expansion

This is an instructive comparison for cities who will host the bulk of urban expansion over the course of this century. Angel derives four propositions of urban expansion from his analyses, a remarkably concise formulation of spatial planning policies for sustainable urbanisation.

The first is the inevitable expansion proposition: that urbanisation is a process that cannot be stopped, only shaped, by effective spatial planning.

The second is the sustainable densities proposition: that in place of the commonplace mantra that cities need to densify, Angel argues that it needs only to be optimised. Cities should be dense enough to sustain a public transport system, but not so dense that they generate health risks for their inhabitants.

Third is the decent housing proposition. 'Adequate housing is possible only when land is in ample supply,' a situation that many local authorities must do a lot more to create. In many cities there is an effective coalition that restricts land supply to generate superprofits for landowners, with severe impacts on the affordability of housing for all.

And fourth is the public works proposition: 'as a city expands, space for public works must be secured in advance of development,' which was precisely Clos' assertion at the beginning of the conference.

For once, it appears that the basic principles of planning for urbanisation have been identified, and packaged in a form simple enough for laypeople (which most politicians are when it comes to spatial planning) can understand. Of course, in a conference as large and fragmented as the World Urban Forum, it remains to be seen whether any urban leaders are willing to listen.

is Editor-in-chief of The Global Urbanist.