Title: Essays on Spatial Economics
Description: The three chapters of my dissertation study factors that contribute to the uneven distribution of economic activities across space. In the first chapter, I study why firms are more productive in larger cities, by focusing on a potential explanation first proposed by Adam Smith: Larger cities facilitate greater division of labor within firms. Using a dataset of Brazilian firms, I first document that division of labor is indeed robustly correlated with city size, controlling for firm size. I propose a theoretical model in which this relationship is generated by both a selection effect---firms endogenously sort across space, choosing different extents of division of labor---and a treatment effect---larger cities increase division of labor for all firms, by reducing the costs associated with greater division of labor. The model embeds a theory of firms' choice of the optimal division of labor in a spatial equilibrium model. Structural estimates derived from the model show that division of labor accounts for 16\% of the productivity advantage of larger cities in Brazil, half of which is due to firm sorting and the other half to the treatment effect of city size.

The theory also generates a set of auxiliary predictions of firms' responses to a reduction in the cost of division of labor. Exploiting a quasi-experiment that changes the cost of division of labor within cities---the gradual roll-out of broadband internet infrastructure---I find causal empirical support for these predictions, validating the model. Finally, the quasi-experiment also provides out-of-sample validation for the structural estimation. The estimated model predicts changes in the average division of labor within different cities in response to the new broadband internet infrastructure, which I find are similar to the actual changes. The second chapter, co-authored with Ariel Burstein, Gordon Hanson and Jonathan Vogel, studies how occupation (or industry) tradability shapes local labor-market adjustment to immigration. Theoretically, we derive a simple condition under which the arrival of foreign-born labor into a region crowds native-born workers out of (or into) immigrant-intensive jobs, thus lowering (or raising) relative wages in these occupations, and explain why this process differs within tradable versus within nontradable activities.

Using data for U.S. commuting zones over the period 1980 to 2012, we find that consistent with our theory a local influx of immigrants crowds out employment of native-born workers in more relative to less immigrant-intensive nontradable jobs, but has no such effect within tradable occupations. Further analysis of occupation labor payments is consistent with adjustment to immigration within tradables occurring more through changes in output (versus changes in prices) when compared to adjustment within nontradables, thus confirming our model's theoretical mechanism. We then use an extended quantitative model to interpret the magnitudes of our reduced-form estimates and to aggregate up the consequences of counterfactual changes in U.S. immigration from the region-occupation level to the region-level. The third chapter proposes a new channel through which improvements in transportation or communications technologies affect skill distribution across space. In this joint work with Yang Jiao, we start with the empirical observations that substantial skill and occupation relocation took place across U.S. cities during past decades.

In particular, big cities attract more skilled workers and become more specialized in cognitive-intensive occupations. Motivated by empirical literature on the association between modern communications technology adoption and production fragmentation, we develop a spatial equilibrium model with domestic production fragmentation to analyze the impact of a reduction in the costs of cross-city production teams---e.g., communications cost---on spatial distribution of skills and economic activities. The model generates predictions consistent with the observed empirical patterns, including more spatial segregation of skilled and unskilled workers, and occupation specialization across U.S. cities over time. In contrast to findings in the international offshoring literature, in which there are winners and losers, we find that under regularities conditions, there are Pareto welfare gains for all agents with heterogeneous skills, together with a substantial measured labor productivity increase at the aggregate level.