In fact, you're right, but is it worth it. In navigation and cartography, I am not very strong. For this it would be better to contact the professionals. There is only one chance to find out - you should pay a visit to the
Galash the Merchant. He has travelled so many seas and oceans, has seen an incredible number of countries and continents. But the main thing - he knows about nautical charts and may know something about ancient marine notations. Go straight to him and show him the plate. You are eager to find everything out, warrior. I admit, i am intrigued also.
Your goal: Bring the plate to Baird the Seafarer and find out from him what it is needed for.
(Dialog at Globius, Pacifist Hills)