Regional specialization, urban hierarchy, and commuting costs

We consider an economic geography model of a new genre: all firms and workers are mobile and their agglomeration within a city generates rising urban costs through competition on a land market. When commuting costs are low (high), the industry tends to be agglomerated (dispersed). With two sectors, the same tendencies prevail for extreme commuting cost values, but richer patterns arise for intermediate values. When one good is perfectly mobile, the corresponding industry is partially dispersed and the other industry is agglomerated, thus showing regional specialization. When one sector supplies a nontradeable consumption good, this sector is more agglomerated than the other. The corresponding equilibrium involves an urban hierarchy: a larger array of varieties of each good is produced within the same city.