Density is Not a Design Decision

+ Alain Bertaud

Joel Kotkin takes “densifiers” to task in a recent post. Kotkin characterizes pro-development urbanists, such as Mayor Michael Bloomberg, as dreaming “of a future where urban dwellers live cheek by jowl in ever-closer proximity.” He advocates instead for lower density development, arguing that it’s better for humanity and more reflective of people’s actual preferences. It is an interesting post that makes some important points, but it ultimately misses the mark.

The higher density versus lower density debate is a distraction. Mayors, planners, professors, and commentators should no more worship at the altar of low density than at the altar of high density. In market-based economies, planners cannot “design” higher density. Higher densities only arise where consumers have a strong preference for a specific place. Design through regulations can keep densities down, for example with minimum lot or unit size restrictions, but the mayor of New York cannot “densify” the city by fiat — absent demand, developers are not going to build towers in which nobody wants to live (unless they build for a captive clientele like public housing).

There is no reason to plan to increase the densities of cities, there is no reason to plan to decrease densities either. When it comes to densities, the market does a reasonably good job of reflecting people’s preferences. Density is simply a land consumption indicator. High land prices tend to reflect consumers’ preferences for a particular location (though in some cases high land prices also reflect land-use regulations that artificially constrain supply). Where land is expensive, the price per square meter of housing will be higher. It’s no surprise then that people consume less land and floor space where land is expensive, which in turn leads to higher densities.

Critics and commentators often confuse density with floor area ratio. Floor area ratio is the ratio of a building’s total floor area to the size of the plot of land on which it sits. High floor area ratios (typically manifested as tall buildings) are not equivalent to high density. In Mumbai the highest densities areas (number of people per hectare) are found in horizontal slums not in high rise apartments. In Shanghai, where the floor area ratio more than tripled since the 1980s, density declined by nearly 20 percent. 

This decrease in densities, even as high-rise buildings multiply, is what my colleague Shlomo Angel demonstrates magisterially in his book, Planet of Cities (cited in Kotkin’s post). Densities are low in Houston because of consumer choices and because of the abundant supply of land. Densities are high in Hong Kong because of a heavy constraint on land supply caused by topography and because of consumer preferences. Housing is cheaper in Hong Kong’s New Territories but some people prefer to spend a fortune to live within walking distance of the Star Ferry.

Floor area ratios are usually heavily constrained by regulations. What Mayor Bloomberg wanted to do in Midtown is to liberalize these regulations and let the market decide what the density should be. There is nothing wrong with that. Anybody who prefers low density is free to live in New Jersey, as I myself do.

I certainly do not advocate high densities, in the same way that I do not advocate wine drinking over beer drinking. I have my own personal preferences, of course. But I find perplexing the extent to which those who are passionate about high or low densities are willing to make policy prescriptions on the basis of personal preference. Where land-use regulations are not onerous, the market will do a good job of reflecting people’s preferences for urban densities—we’ll see lower densities in Houston and higher densities in Hong Kong. One outcome is not inherently superior to the other.

Tile image courtesy NASA's Marshall Space Flight Center.

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