[Pomegranate]

To me it would seem that the case is pretty much exactly as you saw it - the woods with significance are drawn, others are not. One reason could be the thing you mentioned in your first post, Lalwende. For if the woodlands were extensive, as can be assumed, in the format of the "official" maps (I'm assuming the Finnish versions are pretty much the same as the English ones, only the names translated) drawing them all in would've made the map seriously messy. If the maps were in different form - say, for example, that the plains, woods, cities were differentiated by colours instead of little drawings - it would be easier to show the extent of the woodlands. In this format, which is rather unpractical for actual "whole image" purposes, it's better to leave the woods undrawn to keep the map understandable and clear. I think a similar effect can be affecting the hills - I'm pretty sure not all the land outside the main mountain ranges is just flat, but it's just not worth drawing little mountains all over the map.