Multimodal agglomeration in economic geography

Résumé : Multimodal agglomerations, in the form of the existence of many cities, dominate modern economic geography. We focus on the mechanism by which multimodal agglomerations realize endogenously. In a spatial model with agglomeration and dispersion forces, the spatial scale (local or global) of the dispersion force determines whether endogenous spatial distributions become multimodal. Multimodal patterns can emerge only under a global dispersion force, such as competition effects, which induce deviations to locations distant from an existing agglomeration and result in a separate agglomeration. A local dispersion force, such as the local scarcity of land, causes the flattening of existing agglomerations. The resulting spatial configuration is unimodal if such a force is the only source of dispersion. This view allows us to categorize extant models into three prototypical classes: those with only global, only local, and local and global dispersion forces. The taxonomy facilitates model choice depending on each study's objective.