Michael Mehaffy on ‘The need for concentration’ – and the “D” word


Ah, the “D” word, “density” – surely one of the thorniest in the world of planning! But Jacobs takes it on in this chapter with her usual fearless perspicacity.

Translucent Skyscraper by Flickr user 'obeck'

First, she makes the simple observation that the concentration of people within an urban area helps to support a range of specialties offering goods and cultural activities. To support a mix at different times of day, this concentration needs to include residential as well as other kinds of uses. Fair enough.

But be careful, she says, not to conflate high density with overcrowding – as planners have been doing for far too long. Overcrowding is the condition of too many people in a room; it is not too many rooms on a block! As she recounts, there are many cases where overcrowding occurs without high density, and in turn, where high density occurs without overcrowding, in thriving, successful neighborhoods.

How much density is appropriate?  It depends on the context!

“We ought to look at densities in much the same way as we look at calories and vitamins. Right amounts are right amounts because of how they perform. And what is right differs in different circumstances.”

If we accept the idea that suburbs do not need “city liveliness or public life,” then they can make out very well with around six units to the acre.  Semi-suburbs (for example, the classic Garden Cities) might do well with 12 units to the acre – but again, lacking full city liveliness and public life.

But then there is a kind of gap in the density spectrum – a rather problematic range of “in-between densities,” as she calls them – until you get up to about 100 persons per acre and above. It’s only at these higher densities, she argues, that a kind of critical mass is reached where the “constructive forces go to work” to generate the most important urban benefits of density.

Is it possible to be too dense? Of course it is! Densities “can get too high if they reach a point at which, for any reason, they begin to repress diversity instead of to stimulate it.”

High Density in Hong Kong, by Flickr user rc!

Once again, Jacobs reminds us (as she does throughout the book) that no one variable by itself can explain what is going on; we have to look at how the variables are interacting and inter-relating within “an organic whole.” Too much of a good thing is often not a good thing!

Her argument is certainly a cautionary note for those who assume that high density is an automatic evil – but it is equally so for those who have concluded that high density is a magic cure for everything from economic vitality to climate change. Again and again, she cautions us to look at the context, and look at the other variables in play.

For example, just because a standardized kind of building is theoretically able to achieve a beneficial level of density, that hardly means the result will be successful urban liveliness. Here she attacks several common models, including the “towers in the park” model of Le Corbusier (which we also saw her attack in the introduction).

Stuyvesant Town, before and after construction, by Flickr user Hyperakt

The low ground coverages of these project (like Stuyvesant Town in Manhattan) require very tall elevator buildings to get to the densities needed. The result is inevitably a series of buildings that are “most rigidly standardized in rank upon rank.” This is fatal, she says, because “great diversity in age and types of buildings has a direct, explicit connection with diversity of population, diversity of enterprises and diversity of scenes.”

But don’t people need public open space to relieve such high densities? Yes, they do – but the streets themselves, properly designed and energized (with “eyes on the street,” etc.), in fact form these vital public spaces, along with “lively parks in lively places”. And frequent streets (i.e. small blocks) will help greatly in this task.

It’s wrong-headed, she concludes, to think that concentrations of people in cities are inherently a bad thing, or that we can somehow make new self-sufficient towns. That kind of thinking is bad for cities, and bad for the countryside too. Cities are growing, and we ought to recognize and make the most of them.

If we understand how to combine all these dynamic variables, instead of chasing blindly after one or another of them, then we might just be able to get on with the job at hand, of “intelligently developing genuine city life and increasing city economic strength.”

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