What We Do in the Shadows: How Urban Density Facilitates Information Diffusion
Qing Zhang, Evan Plous Kresch
Does urban density facilitate the diffusion of information? This paper exploits plausibly exogenous variation generated by a unique national policy in China that requires all residential buildings to receive sufficient hours of sunshine. The policy creates higher degrees of restriction on density at higher latitudes, where longer shadows require buildings to be further apart. Data on individual housing projects across China reveal that the cross-latitude variation in regulatory residential Floor Area Ratio can be described quite well by a formula linking structure density to latitude through the solar elevation angle. These differences in building density further induce differences in population density and land prices across latitudes. Using differential topic dynamics on a national petition platform to measure information diffusion, this paper shows that people respond to shifts in government attention with varying speeds across latitudes. Increases in local government reply rate to a topic raises the volume of subsequent posts on the same topic, exhibiting an S-shaped time trajectory consistent with local information diffusion about shifting government priorities. These responses are systematically faster in southern cities, where density is higher. Survey evidence further indicates that otherwise similar individuals are more likely to gossip about public issues in a southern city.
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