I'm curious how the dark skies map is actually built. I assume it tries to make generalizations based on density of buildings. And that is only as accurate as the building data is in the map source.

It's probably fairly accurate overall, but there is undoubtedly some region-specific things (different lighting styles, etc) that throw a wrench into the mix.

One place out my direction has a blue blob in the middle of a dark gray area, so you wonder what kind of civilization is there. Nothing, just a few buildings that are uninhabited and unlit. So there's no light pollution in actuality, but dark skies thinks there is.

They are based on nighttime satellite photos. The downside of that is its only based on the light that gets through the atmosphere. So a dusty/humid place will have a lot more light pollution than the map shows because the dust blocks the light from the satellite, and reflects some of that light towards an observer on the ground.

I live in the western USA where very dark sky areas are abundant. After reading your comment, I was curious to see what Europe looked like. I was astonished that not just Europe, but the Eastern USA also, has no very dark sky areas at all. It is amazing how populated these regions are.

But, then I go down to Australia and nearly the entire continent is great for sky gazing (other than all the critters trying to kill you).