Phew - lots of misinformation in this thread, let's see if I can clear it up.
Civ4's AI does not know the location of hidden resources, nor does it see the full map (as has been claimed here). We tested this right after release because these rather obvious AI cheats were a big issue for many of us with the Civ3 AI - it was quite aggravating to see the Civ3 AI settle in the middle of the desert because it
knew there would be oil later, and it was quite hilarious to exploit the Civ3 AI's knowledge of the map by "channeling" its attack forces into endless loops. We were pretty glad when we saw that these issues did not happen with the Civ4 AI.
We did some (imho) pretty solid tests on alleged AI cheats in
this thread. Note that at first we actually found out that the AI _did_ "see" hidden resources under certain conditions (which were unlikely to happen in a real game), but that was a bug, which Soren promptly fixed.
Side note: No offense, but I really wonder why people keep making obviously false claims without testing them. I mean, I would feel pretty bad if I stated something like "The AI sees / doesn't see the resources" as a fact without either checking it myself before, or making sure that the claim is based on a reliable source. Checking it by oneself is quite easy to do with the worldbuilder.
In case you wonder why I'm addressing this: I believe that such false statements about the AI are one of the reasons why Civ5 has such an abysmal AI. You can listen to Sid Meier talking about game AI in his GDC 2010 keynote address, he says that an AI must not be too clever because the player will just say that it cheats. (Source:
here). Civ4 has a pretty good AI that removed many cheats that the Civ3 AI still had - but people are still just saying that it cheats when it does something well. The logical conclusion for game developers is that
it doesn't pay to develop a very good AI because lots of players will simply refuse to acknowledge it. Therefore it's much more cost efficient to develop a game with a weak AI -> see Civ5.
So, next time you state as a fact that the Civ4 AI is cheating with something, do actually test that, okay?
