Maps makes everything better
I like maps so all games should try to have them. It should be against the law to make a fantasy game without a map. Maps even help when you are looking for a job where you can make games with maps. Maps is a win, always.
World vs Area
The map is often split into two modes, the world view and the local view. The world view show the whole world or at least the parts the player has explored and the local view show the area around the player at the moment. Zooming our switch to world mode and clicking on a place in the world zooms in to local view.
Fog of war
Fog of war is the way to hide the map areas where the player has not been. To goal is to show what places that remain to explore. Skyrim shows the whole world map but the lack of explored markers in the area show the player that he has not been there.