Solid Idea. Here are some thoughts on it:
I think it makes more sense to show hazards even if you haven't scouted the area - or would we like the hidden dangers of the map to reach out and 'thwack' the unsuspecting? This could go either way, but definitely something to think about.
Hazard rating could have a malus rating for population growth for cities (check the hazard rating on the central tile?). This reflects people's unwillingness to move into more dangerous areas, even with the support of the nation. It takes a special kind of person to be willing to dive out into the great unknown.
It's possible that such a setup is "farmable" for sovereign and army experience. Is this something we should be worried about?
Would/Should hazard ratings effect the pathing of roads and caravans?
Your hazard map has gotten me thinking about a UI change... *scurries off to go write that up.*
Well, ideally you would not want to show the hazard influence until you've scouted, otherwise hazard zones will be a sort of back door way TO scout (after all, if you see a nasty hazard radius then you know that there is a big dungeon nearby.) And besides, not showing hazard radius until you've scouted the source buffs the meaningfulness of actually scouting.
As for farming hazards, the best way to handle this is to make each hazard act in its own best interest. For instance, a band of Goblins would look at the mighty archer-studded fortress and say, "You know what, maybe we should pick a softer target." Baddies would generally only attack when they had a fighting chance, and they wouldn't generally raid a city to destroy it. They would probably attack and begin to "steal" from the city as the melee continues, then retreat once they've gotten their fill. Fail too often in defending a city and it eventually is burned or disbanded. Want to eliminate the raids? Then you have to go destroy the source.
On the other hand, if a cave of trolls or a village of goblins see your city's army vastly outgrow their forces, they might eventually just pack up and travel elsewhere. In one of my earlier posts, these kinds of hazards were actually rudimentary AI's that had their own little mini nations, but could never grow as mighty as a late game sovereign kingdom. So a lot of those hazards might even be quarelling with one another.
