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The Topography of Metropolitan Employment: Identify Centers of Employment in a Polycentric Urban Area

Christian L. Redfearn
Increasingly, U.S. metropolitan areas are polycentric. While this is well recognized, there is lit- tle consensus as to the appropriate method for identifying centers of employment and their extent. Discussions of sprawl and decentralization, agglomeration and productivity, and the impacts of transportation or land-use regulation on urban structure depend crucially on the spatial account- ing of employment within a metropolitan area. Existing methods for subcenter identi¯cation su®er from strong assumptions about parametric form, misspeci¯cation, or reliance on local knowledge to calibrate model parameters. Using data from the greater Los Angeles metropolitan area, this paper introduces a nonparametric method for identifying subcenters { both their centroids and bound- aries. This method is benchmarked against representative alternatives for subcenter identi¯cation. The importance of the di®erence in approaches is made clear by comparing their measured con- centration of the greater Los Angeles metropolitan area. Results indicate that this, more °exible, nonparametric approach yields both greater accuracy in de¯ning subcenter boundaries and better resolution identifying a wide range of subcenters. These attributes should better inform research that employs density as an independent or dependent variable.