Measuring urban sprawl: some results

I measure sprawl by looking at the pattern of development in the suburban portions of 59 large urban areas in the United States (see my earlier post).  I have delineated the urban areas for the census years from 1950 to 2010 using census tract data for housing units. Urban areas are defined as the contiguous tracts meeting a minimum density threshold in much the same way that the Census defines Urbanized Areas. The suburban areas are then defined as consisting of those tracts added to the urban areas after 1950.

Multiple measures of density in the suburban areas are used for the creation of the sprawl index. These include density, housing-unit-weighted density, and the percentages of housing units in census tracts with densities less than the first density quartile and the median density for all of the suburban tracts. Standardized scores are used to combine these measures into a single sprawl index for 2010.

First looking at which areas sprawl the most: Greenville-Spartanburg, South Carolina tops the list. But sprawling areas are not limited to the South, as Albany-Schenectady-Troy comes in second. And they are also not limited to the smaller urban areas in the dataset, as Boston-Providence is the eighth most sprawling of the 59 urban areas, which may be a surprise to many. But remember we are not talking about the very urban environments of Boston or Cambridge, we are talking about the levels of sprawl in the suburban areas developed after 1950.

The least spawling areas will be equally surprising. Las Vegas has the lowest level of sprawl, followed by Miami-Fort Lauderdale-West Palm Beach. And Los Angeles and Phoenix, areas seen by some as exemplars of sprawl, are the areas with the fourth and fifth lowest levels of sprawl.

Looking at the means of the sprawl index for the areas in the 4 census regions, average levels of sprawl are by far the highest for the areas in the Northeast. And they are equally low for the areas in the West. Areas in the Midwest and the South have mean levels of sprawl closer to the overall mean for all areas.

One factor that may be contributing to lower levels of sprawl in some areas is the presence of physical barriers to the expansion of the urban area. Urban areas up against mountains and wetlands had much lower levels of sprawl than other urban areas.

For those questioning this approach to measuring sprawl because it places Boston as high sprawl and Los Angeles low, consider this: The suburban areas around Boston had a density of 584 housing units per square mile. For Los Angeles it was 1,335. And 46 percent of all suburban housing units in Boston were located in tracts with densities less than the median for all of the urban areas, 611 units per square miles compared with only 9 percent for Los Angeles.

More on the measurement of sprawl and these results can be found in my paper, “An Alternative Approach to the Measurement of Urban Sprawl” which can be downloaded here.

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