By perceiving state borders to be physical barriers that keep disaster at bay, people underestimate the severity of a disaster spreading from a different state, but not the severity of an equally distant disaster approaching from within a state. We call this bias in risk assessment the border bias.
More here. Amusingly, the authors show that making the border more salient by darkening the border lines on a map can make people feel even more protected.
Hat tip: Paul Kedrosky.