I like what you've done here. I certainly wasn't expecting to see a Runescape mod for CK3, but it actually makes pretty good sense. You've gone done an amazing job of porting the Runescape landscape into CK3, but one thing bothers me greatly:

The Runescape map overlay is painted on the world textures. This doesn't look very good as it is now. Also, when in the second-farthest zoomed-out map mode, the realm colours completely cover the map, making it difficult to know what part of the world you're looking at.

I don't know if it's possible to mod this, but I would change the "Realm colour" map-mode to be more transparent, so you can see either the terrain, or the RS map underneath. Also, I would make the RS map either more prominent in the Terrain map-mode (the most zoomed-in mode), or model the RS map in-game (houses, etc), but to my knowledge that is very hard if not impossible to do in CK3. Also it would be very time-consuming.

I hope you continue to work on this, as the idea of a RS mod in CK3 is very interesting to me.