While I only know enough computer stuff to destroy one, I've been reading thru these posts and was thinking about the old "Distomap" Rand McNally that we used to use as dispatchers. If the numbers were put in a circle, and then the holes punched as in the hidden flag pic, perhaps that would be a key?
Distomap for sale here…
https://www.amazon.com/Distomap-Rand-McNally/dp/0528883690