Measuring two decades of urban spatial structure: The evolution of agglomeration economies in American metros.

In this paper we examine the evolution of urban spatial structure in U.S. metropolitan areas over nearly two decades. Using annual block-level data from the Longitudinal Employment Household Dynamics database, we introduce a technique for identifying regional employment centers that both adheres to urban economic theory and pays homage to classic contributions in local spatial statistics. Centers are defined as local spatial statistical outliers on the network-based job accessibility surface. We proceed by identifying the location and employment makeup of centers for each metropolitan region in the USA from 2002 to 2019 and discuss emergent trends across time and space. Critically, we not only explore empirical patterns, but we discuss the relationship between polycentricity, the evolution of urbanization and localization economies, and regional specialization. We confirm again the pattern of polycentricity in U.S. metros and show that the structure of metropolitan employment is largely stable over time. We also document a continuing trend away from urbanization economies into more specialized subcenters. • We develop a new technique for identifying employment subcenters combining spatial statistics, network analysis, and computational geometry. • the technique generates bespoke polygons that can be used for further analysis or designated as targets for urban development. • We apply our method to 20 years of annual census block -level employment from LEHD and discuss the trend toward increasing polycentric development in the U.S. • We document the increasing prominence of more specialized localization economies. • The methodology we contribute is generalizeable and can be applied anywhere in the world (we provide a Python software package for reproducing the results) [ABSTRACT FROM AUTHOR]