Here is also a quick-reference sheet just to give you an idea of what can be done with map commands.
http://www.dom3minions.com/docs/map_qref.txt
And if you really dive into map commands then be sure to look into the SemiRandom program by Ballbarian. It uses map commands to scatter surprise provinces around a map. Using map commands you can design a logical themed province where the name of the province, the units guarding it, the magic sites there, etc all make sense together. A town of undead, or a forest grove of birds, or a dragons den.
The SemiRandom program also uses map commands to randomly assign designed gods for AI. Instead of the random ones the game makes (which can be surprisingly good or surprisingly stupid) you can run a map thru SemiRand and get a god assigned that was specifically designed for that nation. The God, the magic choices, the scales, and even some extra equipment assigned to it in order to give it a good boost above vanilla AIs
If you want to check out what SemiRandom does there is a downloadable map on my site called Aran_dom, or you can play in one of the SRAND games on the server
http://www.dom3minions.com/maps.htm
http://www.dom3minions.com/HostedGames.htm