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Sprawl Index


Sprawl is an important environmental issue, and in some previous posts I looked at national and Missouri data on sprawl, and at some maps that showed a picture of how land was used in Missouri. (The first post in the series is here.)

In order to study sprawl, it is useful to have a single number that represents how sprawled a region is. However, sprawl consists of a number of related characteristics. In 2002 the first compactness indices were developed using data from the 2000 census (compactness is the inverse of sprawl). The report contained index values for metropolitan statistical areas (MSAs) and metropolitan counties across the country.

That work has recently been updated using data from the 2010 census. This report presents the rationale for how the new indices were developed and the methods used. This report also contains tables of index values for MSAs, metropolitan counties and smaller urbanized areas, and it compares values from 2000 with those from 2010.

Both indices are normalized so that 100 is the mean, with lower values indicating more sprawl and higher values indicating more compactness. Specific values do not conform to any particular reality. So for instance, if one MSA has an index value of 70, while another has a value of 140, it would not mean that the second is twice as compact as the first. I’m not sure what “twice as compact” would mean, anyway.

Compactness of MO CountiesThe indices combine 4 types of factors: the first is based on the density of the region (the most important), the second is based on the degree to which the region is separated into single use sub-regions or has mixed use throughout the region, the third is based on the degree to which dense areas cluster in one central core or are spread throughout the region, and the fourth is based on the block length and intersection density of the streets.

The most compact county in the USA is New York County, NY (Manhattan, no surprise there). The first table at right shows the overall Compactness Index plus the 4 factors that make it up for the 29 metropolitan counties in Missouri. They are ranked by the Compactness Index. As you consider the table, don’t forget that the counties differ from each other in many ways aside from compactness. For instance, St. Louis City is very different from Lafayette County or Washington County. Simply comparing their compactness scores would not be an apples-to-apples comparison.

(Click on table for larger view.)

Compactness of MO MSAsThree MSAs in Missouri are on the list. The second table at right lists them, their Compactness Index, and their factor scores. While the City of St. Louis was the densest county in Missouri, Springfield is the densest MSA. This surprising result may come from the fact that between 2000 and 2010 the St. Louis and Kansas City MSAs were redefined. The St. Louis MSA now includes 16 counties, while the Kansas City MSA includes 15, and the Springfield MSA includes 5. This, again, shows the difficulty of comparing regions. I’ll have more to say on this in the next post.


Ewing, Reid, and Shima Hamidi. 2014. Measuring Urban Sprawl and Validating Sprawl Measures. Salt Lake City: Metropolitan Research Center, University of Utah. Downloaded 6/13/14 from http://gis.cancer.gov/tools/urban-sprawl/.

Spreadsheets with the county and MSA data are available for download at the same URL.

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