  We simulate a spatial behavioral model of the diffusion of an infection to
understand the role of geographic characteristics: the number and distribution
of outbreaks, population size, density, and agents' movements. We show that
several invariance properties of the SIR model concerning these variables do
not hold when agents interact with neighbors in a (two dimensional)
geographical space. Indeed, the spatial model's local interactions generate
matching frictions and local herd immunity effects, which play a fundamental
role in the infection dynamics. We also show that geographical factors affect
how behavioral responses affect the epidemics. We derive relevant implications
for estimating the effects of the epidemics and policy interventions that use
panel data from several geographical units.
