Dear AudaciousTUX, i have to disappoint you, earth in fact is not spherical. It's flat.
No, im just joking, its not flat but its also not sperical, its flying through space on the back of a giant turtle.
Ok, thats also not the truth. In fact earth has potato shape (its a Geoid).
Concerning the flat map, well earth curvature doesnt need to apply to it, because earth is too big and 0ad maps are too small to even notice it. That is if you want to apply earth curvature to 0ad maps with realistic proportions.