According to the Wiki, Spies is a technology which
allows a player to see their enemies' Line of Sight.
And Cartography:
allows a player to share their allies' Line of Sight.
In this case, if I research Spies, will my ally be able to see my enemies line of sight? If yes, we could split the required gold
Best Answer
Cartography only provides vision of allied units. Spies provides vision of all units. So, if your ally has Cartography, they can see your units. Because the units that you see with Spies aren't yours, your ally can't see them.
Remember, Cartography doesn't actually share all allied vision, it just grants you the vision of any allied unit.