The Map Room: Darker Than You Think
the original Light Pollution Atlas was systematically biased by the fact that snow was on the ground when the underlying satellite measurements were taken. Lorenz recalculated the light pollution for the U.S. and southern Canada based on snow-free satellite observations, and the whole northern part of the area came out roughly one full zone darker. That means that the original atlas overestimate the skyglow in this area by a factor of three.
Even so, the Bay Area sticks out as a red spot. At least there are some good dark skies within a (relatively) easy drive. (via aemkai’s ffffound)