It's Harold Fiske's Mississippi river map that shows how the Mississippi river changed over time, combined with a watercolor style transfer.
It's also the cover of one of the first set of LessWrong books that we published: https://www.lesswrong.com/books/2018
I think an important aspect to mention explicitly is that it's paired with the phrase "a map that reflects the territory". It's important not because Harold Fiske or the Mississippi River are important to rationality, but because this image exemplifies the idea of that a map is meant to help you understand and reason about something that is not the map.
I was not aware that we had published any books!
A few questions:
When I had the same question a while back, the conclusion that I came to was that it was a picture of a map, depicted on a billowing flag (or piece of cloth), and flags are usually planted somewhere to mark a territory. Thus, it is a map which is used to alter (or become part of) the territory!
What am I even supposed to be looking at here?