Hi, Mimine
In addition to what has been said, maybe one sollution (I believe the problem may be the border between the south and north continents) would be to show this connection twice, once in the north, once in the south? (I know it is weird to feature the same thing twice in a map, but they could be two maps, one made by a northern nation, one by a southern nation, anyway, just ideias). Furthermore, keep things simple? Like, using icons and stuff. Anyway, I don't know.
Now, for examples, your size demand reminded be of the pulp books, 17.4 x 10.4 x 1 cm. I know the Pellucidar map, by Edgar Rice Burroughs series (it is from 1915, so it is outdated but anyways, also it is already public domain so I will leave it here).
Pellucidar.jpg
Also the Game of thrones map in the books, it is really concise and precise.
https://atlasoficeandfireblog.files....-north-map.png
https://www.reddit.com/r/gameofthron...he_books_only/
Hope it helps.