I use DarkSiteFinder [1], to find dark spots for astronomical viewing. It's really depressing how far I have to go in the Midwest! to get to a "dark" sky. Depressing!
Based on a few trips to the Pawnee Grasslands this summer, I can say that lightpollutionmap represents the state of the night sky better than darksitefinder.
What data is this map based on? Just population density?
This map doesn't appear to reflect e.g. airports with a lot of light pollution.
There is a write-up of this site at cloudy nights. Ill try and find it.