A low-fantasy GSG could be done with a limited "known" area around you, with decreasing information the further away you look. There could be 3 or so "levels" of information about provinces and countries, with a decreasing initial level of knowledge over distance or hostile border.
Neighboring provinces would be clearly known (level 3), and show fairly detailed information, becoming less known beyond that (level 2 for the next friendly province or two, fading to level 1 at some distance). All neighboring countries' distant borders would likely be at least marginally or partially known (perhaps with the possibility of a few unknown provinces), and you'd probably know at least the names of any major countries on the other side of their border, with a random chance of knowing any smaller one. Distant major countries would probably be "known" only as a name and general direction, which could be done by only displaying one random province of that country and giving it the name of the country and no other info, so you'd know where to find it, but not much else about it.
Consider Europe's knowledge of China in the Dark Ages. They knew "roughly" where it was (the route to it had been recorded to some limited extent, but China's actual position on a map was more than a bit vague), and it was possible to trade on a very limited basis over the immense distances, but its borders were unknown, and most other information about it was more legend than fact.
You don't need to present the entire map as "fact", only your immediate surroundings and a few scattered bits and pieces which would be significant enough to have drawn attention. Exploration would clarify the vague information and expand your area of knowledge, while occasionally making another distant province or country "heard of", rather than "known".
It SHOULDN'T behave too much like a standard "4X" game, because it wouldn't be one, more like a hybrid of one.
