I was thinking that too, and was fully expecting the top comment to be a joke about heat maps that are actually population maps, but it turns out there are some

I was thinking that too, and was fully expecting the top comment to be a joke about heat maps that are actually population maps, but it turns out there are some interesting insights I wouldn't have expected. Namely that there are substantial differences when comparing areas with light pollution legislation with similar unregulated areas; also interesting to see how much light pollution there is even at sea!