What are the mysterious light sources on light pollution maps?

One thing I'd like to see is a light-pollution map of the US overlaid with a map of all US federal land. To answer the question: what's the brightest thing the federal government is doing?

I was looking at light pollution maps just the other day, trying to find places to do astro-photography, and was blown away by how much light pollution there is. Really sucks, because I'd have to drive about 90 minutes out to get into a dark zone.

I flew through the night to Singapore once. I remember two very striking light sources.

Firstly, oil well flares in the Middle East. The oil fields are in the middle of nowhere, so they're these huge orange-red blooms set in utter darkness.

Secondly, Delhi. The city is brightly lit with streetlights. But there's a suburb (?) to the south, Faridabad, that's as brightly lit, but with a different, whiter, kind of lights. So you had these two huge blotches of yellow and blue light projecting into each other. There are also some extremely bright areas to the south of the city - after some investigation, I decided they were probably rock-crushing plants.

Ah yeah, in the post's first "unknown light pollution" example, I figured it must be a greenhouse. I was driving through a relatively small town one time and was a bit freaked out by this ominous yellow glow off in the distance. Like, the whole sky was glowing [0]. I ended up driving out to try to find the source, and discovered it was a huge greenhouse/farm. Luckily not an extraterrestrial landing zone or so on ;)

[0] looked like this https://i.cbc.ca/1.4925044.1543460834!/fileImage/httpImage/i...

Only 90 minutes? For me it's at least 3 hours to get to Class 4 on the Bortle scale. Class 2 is probably more than 5 hours. Only alternative is the sea.

I'm planning to take a trip to a Class 1 this summer, it'll be hard to find a place that dark that is reasonably reachable though.