Hello everyone!
We are currently looking for information about this grid map, and since you guys are very knowledgeable in this field I figuered I'd ask you about it. We want to use it in the game, but we are unable to find any information on where to find a high resolution version of it as well as information regarding copyright issues. I have been looking around on the forum as well, but I've not managed to find anything about the actual source of the image.
We are also looking for other versions of it covering the areas missing in this one such as the Baltic Sea.
If you guys know anything about a museum or private collector who has it we would be very grateful!
Image:
https://anjns.home.xs4all.nl/subsim/kmgridlarge.jpg
/Einar