Map information is basically offering them the map of the portion of the world you've discovered/can see. This mostly consists of your empire, but will include any areas that have been seen by your various agents and armies. Similarly, by getting map information from other factions, you can uncover areas of the map where they have been but you have not. This is most useful for determining where the heck cities are on the map, but good for other things as well like resource locations, and to determine the spread of various factions that you normally wouldn't know.