Strangers in our midst: the usefulness of exploring polycentricity

The existence and persistence of cities provide prima facie evidence of agglomeration economies, but do little to inform our understanding of the specific nature of forces that induce the concentration of economic activity, nor the spatial scale at which they occur. Though the theoretical literature on conceptualizes these forces without specific geographic scale, the empirical literature largely treats them as working mainly at the metropolitan level. We argue that agglomeration may work at different spatial scales. There is now extensive evidence that metropolitan areas are polycentric, with a significant portion of employment clustered in employment centers outside the CBD. This provides basic evidence of net agglomeration benefits at the sub-metropolitan level. We explore theories of agglomeration and consider how they may explain the presence, location, characteristics, and growth of employment centers. We illustrate the usefulness of exploring polycentricity with a case study of the Los Angeles region. Our understanding of agglomeration economies can be enriched by investigating the nature of employment centers and the forces that produce and sustain them.