I have found one ...
peculiarity with the design of this map that I find to be at least a flaw of logic (in the sense that the effect isn't logical).
Specifically, the way most rivers are made into unpassable barriers between provinces seems to break the flying races and Vanheim.
I know it's a side effect of how 'barrier' borders are implemented, but it just doesn't make sense that flying armies couldn't fly over the rivers.
Similarly, the Vanir can sail their armies across vast oceans - but not across a river? This is a cognitive dissonance, imo.
I don't know that it needs to be fixed, or for that matter that it can be fixed (short of Illwinter implementing three grades of unpassable borders: impassable to land / land + sailing / all movement ). But it is something to keep in mind when choosing Pretenders and nations for the map, as Caelum and Vanheim lose some of their normal benefits.
Still, a great map.
Oh, side note: 129, Blackwater Ruins is a "magic rich" province, but with magic sites set to 60, heavy searching (903131140) has revealed nothing. Looking at the map file, I'm guessing that the
#terrain determines likelihood of magic sites? Is #terrain type 1568 actually something magic rich, and simply bad luck in this game?