Inkweed needs more ways to be gotten. Grassland is just too rare. First off, it should be growable, but will die 70% of the time before it can be used. Another way is that it sometimes can appear in shallow water, floating along. And occasionally it will appear in the water when digging for clay. If not, there should be substitutes of ink and parchment. On runestones, you should be able to use a rock to carve a map of the local area onto it. Or you can use clay instead of ink, but will only show rivers, forest, and grassland, making very crude maps. Just a thought.
Also, there should be minor distortions in the maps when made, with less the higher quality. Like that river is too wide, or that grassland is more south. Perception and exploration would both improve map quality. Just a thought!