Sir_Lancelot said:So why do they love to trade maps so much..?
They do not know the map perse, they know the tiles. That is to say that they know what is on a given tile, be is a resource or your units. They do not know the map in an aggregate. IOW they do not know how to get to that oil they know if onver on ytonder tile.
They need to explore the are or get a map to be bale to find the way to that oil. It is a convuluted mechanism, but it is what we have. Just like you know the captiol of a civs is located at X, Y or Z after an embassy is build, but it could be in fog as you have no knowledge of the map.