Well, I don't know the specifics, but basically we start the faction off with a number of spies, who are exterminated with a script before play begins. Thus their initial map reveal remains, but they're not available to the player.

It basically has the effect of revealing a select portion of the map to the player, representing factional knowledge gained through trade, invasions, and so on. Theoretically we will have one set of this for each faction in the final release, though that requires people to define what areas need to be viewable for each faction at the beginning. And, of course, more scripting help so that we can pick up where we left off.