A Melitz-style model of monopolistic competition with heterogeneous firms is integrated into a simple new economic geography model to show that the standard assumption of identical firms is neither necessary nor innocuous. We show that relocating to the big region is most attractive for the most productive firms; this implies interesting results for empirical work and policy analysis. A 'selection effect' means standard empirical measures overestimate agglomeration economies. A 'sorting effect' means that a regional policy induces the highest productivity firms to move to the core and the lowest productivity firms to the periphery. We also show that heterogeneity dampens the home market effect.
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