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

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.