What would the total population be? 400,000, spread across a few major cities and the countryside?

I'm not sure I like the idea of four completely stereotypical nations, each one with one type of resource in abundance. Too much like Avatar: The Last Airbender. The basic premise is fine, I'd just prefer more unique groups for the sake of a better story. 

Maybe a loose khanate of nomadic tribes would have access to wind and nature magic, with various shamanistic rituals to commune with the spirits for guidance or help, and a tiny portion of their population born with the ability to wreak havoc by calling upon the magic powers of their tribal spirits. This tribe would have the least amout of magic, however what they do have would be powerful. I can see these people controlling a relatively large swathe of land, but with a low population due to their nomadic nature. Inspired by the Mongols and a bit of the Klug tribe, technologically wise they might not be superior but through the use of clever tactics and what magic they have, they would make a surprisingly formidable opponent.

What do you think? We don't even have to use that; I just wanted to make the point that four mostly equal nations that neatly fall into the four categories of stereotypical magic seems too gamey. Just like we have the OP urge players to make interesting and unique characters and creatures, the NPCs and plot characters especially need to be interesting as well. But then again, I could be the only one who feels this way.

Also, as I mentioned in my previous post, we should figure out who will be the GMs.

Edit: Come to think of it, I don't think four nations, each fiting nicely into one corner, is ideal. I say we have five, with this fifth one being a kingdom with a massive and wealthy capital, smack dab in the center of the map. Such a prize would be very tempting, so naturally I think we might see two or three Keepers straying from their edges of the map towards the middle in an attempt to sieze it. The more things we can do to encourge interaction, the better. A central location would also be a good place for plot actions to go down.