  In the face of elevated pandemic risk, is it necessary to completely lock
down the population, imposing extreme social distancing? Canonical
epidemiological models suggest this may be unavoidable for months at a time,
despite the heavy social and human cost of physically isolating people.
Alternatively, people could retreat into socially or economically defined
defensive zones, with more interactions inside their zone than across zones.
Starting from a complete lockdown, zones could facilitate responsible reopening
of education, government, and firms, as a well-implemented structure can
dramatically slow the diffusion of the disease. This paper provides a framework
for understanding and evaluating the effectiveness of zones for social
distancing.
