  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.
