The “what’s your map” podcast has this gem of an episode.
Smuggling Silk: WWII Escape Maps with Dr. Barbara A. Bond
“Together, they pour over an important but unassuming silk escape map of Danzig (Gdansk) port from World War II. What information is presented on the map, and what has been intentionally excluded?“
The show notes has a link to the map, which you really should peruse while you’re listening to it.