Spatial scale of agglomeration and dispersion: Number, spacing, and the spatial extent of cities

Abstract: Cities around the world have become fewer, larger, and more spatially dispersed. We offer a theoretical framework that can account for this dual transformation - economy-wide concentration and local spreading - by distinguishing between two types of dispersion forces: "local" forces acting within cities, and "global" forces acting across them. The distinction leads to a systematic classification of spatial models into a few fundamental types, each entailing distinct spatial patterns and comparative statics. The framework serves to reconcile divergent empirical findings and clarifies how spatial outcomes of transport policies may depend on the spatial scale at which relevant dispersion forces operate.