A theoretical framework for evolutionary economic geography: industrial dynamics and urban growth as a branching process

We propose a framework that specifies the process of economic development as an evolutionary branching process of product innovations. Each product innovation provides a growth opportunity for an existing firm or a new firm, and for an existing city or a new city. One can then obtain both firm size and city size distributions as two aggregates resulting from a single evolutionary process. Gains from variety at the firm level (economies of scope) and the urban level (Jacobs externalities) provide the central feedback mechanism in economic development generating strong path dependencies in the spatial concentration of industries and the specialization of cities. Gains from size are also expected, yet these are…