Does Spies provide Line of sight for my Ally with Cartography?
Solution 1:
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.