URBAN SPRAWL is measured as a combination of four factors, representing four distinct dimensions of sprawling development patterns: development density, land-use mix, population and employment centering and street accessibility:
Development Density which is the most widely studied dimension of sprawl. In this study the density factor is measured through six distinct but related indicators: 1) gross population density; 2) percentage of the county/MSA population living at low suburban densities; 3) percentage of the county/MSA population living at medium to high urban densities; 4) gross employment density; 5) net population density of urban places within the county/MSA; 6) estimated central density of metropolitan areas derived from a negative exponential population density function (only MSA level).
Land use Mix accounts for the degree of mixed and integrated land uses and is measured through three indicators: 1) degree of job-population balance; 2) degree of job mixing; 3) average Walk Score within counties and metropolitan areas.
Population and Employment Centering accounts for the role and significance of main centers and urban sub-centers in shaping the overall structure of counties and MSAs. It is measured through five distinct indicators: 1) degree of variation in neighborhoods (census tracts) population densities within the county/MSA; 2) degree of variation in neighborhoods (census tracts) employment densities within the county/MSA; 3) percentage of the county/MSA population living in main or sub-center; 4) percentage of the county/MSA employment reside in main or sub-centers; 5) density gradient variable showing how quickly population density declines from the center of the MSA (only MSA level).
Street Connectivity accounts for the degree of street network connectivity in the county/MSA and is measured through five distinct indicators. The first three indicators are related to block size since smaller blocks translate into shorter and more direct routes. They include: 1) average block size; 2) percentage of the county/MSA small urban blocks; 3) average block length (only MSA level). The last two variables account for the number and type of intersections: 4) intersection density; 5) percentage of 4-or-more-way intersections in the county/MSA.
Overall Score
The four sprawl factors were weighted equally and combined to an overall index for 995 metropolitan counties as well as 202 medium-sized and large metropolitan areas and 13 metropolitan divisions in 11 largest metropolitan areas. More than 281 million Americans, nearly 85% of the United States population, lived in these 995 counties in 2020. The average value of the overall score is 100 which means the more compact counties/metro areas have an index value of above 100, while the more sprawling areas have an index value of below 100.