chosing a map for minimal lag?

[Snerk]

I was just wondiering if there is anything besides the size of the map that determinds how much of a slow down im going to have in late gameplay.
For my pc, i shouldn't play on anything else than Small. However, i've noticed that many of the worldbuilder files has different filesize even when they are of same mapsize. So in short, what determinds lag: Map size?, worldbuilder filesize?, both?, or something else?

 

[robaughjr]

Both, and the number of ai civs also as the computer needs time to "think" about each ai unit's move.