Not too long ago I received an email from someone asking me to help them define the term “urban sprawl”.

The message was not completely clear, but I took it as coming from  someone concerned that a development near their home would negativity impact them and they asked if there was a way to define urban sprawl.

At that time, I told them that there was no clear definition for urban sprawl and that this term was loaded with political implications I wanted to avoid.

In a previous article I shared my impressions on Vishaan Chakrabarti’s talk A Country of Cities: A Manifesto for an Urban America.  Chakrabarti’s talk reminded me of this email, and as he proceeded to make his argument for hyper-densification, a clear definition for “urban Sprawl” started to emerge.

Chakrabarti says that the density breakpoint where high speed rail becomes viable is 30 dwellings per acre.   According to Chakrabarti this level of density is high enough to support ridership for mass rail transit.  He also points out that only 12% of US cities have zoning regulations to support this level of development.

In lay terms, “urban sprawl” means the uncontrolled expansion of urban areas.  The implication here is that as urban environments spread they spread into areas which were once considered rural.  This expansion of the built environment fosters growing “suburbs” that are characterized by low density residential housing and single-use zoning.

For those opposed to urban sprawl, they argue that urban sprawl has a negative impact on the environment.  The claim is that as suburbs expand they reduce the amount of land available for agriculture.  Urban sprawl is also tied to increased water and air pollution, and wide spread housing associated with urban sprawl creates a dependency on cars which increases traffic.

I like how Chakrabarti uses dwellings per acre as a measure, but I’ve also seen geographies defined according to total populations.  “Urban areas” are defined as geographical areas such as towns, cities, and metropolis.   The population of a metropolis is over 300,000 people, the population of a city is between 100,000 and 300,000 people and the population of a town can range from 1000 to 20,000.

Villages and hamlets are geographical areas of lesser quantities and as such are considered to be “rural areas”.

Defining geographies in this way does not tell us much about density which is at the hearty of the term we are seeking to define.

Along with his definition for hyperdensity, Chakrabarti claims that geographies where the density is 3 to 4 dwellings per acre or less constitute 83% of the United States.

With these figures in mind I would say that urban sprawl can be defined as single use residential developments with a density of 3 to 4 dwellings per acre.  This is as close to an objective definition as I have been able to find.

Developments of attached single family townhouses fit this definition and therefore would be considered a form of urban sprawl.

Whatever your position is on urban sprawl and regardless of whether you prefer to live in an urban area or a suburban area, we now have an objective definition.

The truth is that populations are exploding all over the world and as each generation grows in affluence, the demand for affordable middle class housing will continue to grow.

We don’t all want to live in massive housing units stacked on top of each other with neighbors on all sides.  We can’t all afford to buy an acre of land near where we work.  Town houses are an affordable ways to step away from city centers and enter into home ownership.  So while these forms of developments are often maligned, they do serve a valuable function.

As long as populations continue to grow and as long as we continue to be upwardly mobile, people will continue to migrate into and out of cities.  With this migration we can expect housing to spread into rural areas.

I’m not going to offer a judgement on whether this is good or bad.  All I know is that the need exists and now you have information to define this form of expansion.

What do you think?  Is urban sprawl a problem we need to stop?  Or is urban sprawl a sign of social progress?  Tell me your stories.

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