Perhaps some varieties of wizard (Read: Those who use magical spheres that are based on an Alignment [Good, Evil], a form of change [Decay, Corruption, Life, Death], or other, similar factors) should gradually change the land surrounding their Tower/Demesne/Territory.
For example, Urist McGodlyWizz, a master wizard tied to the Spheres of Wealth, Change, and Greed, might gradually change the stone below his tower to be filled with valuable minerals simply with his presence. Perhaps due to the influence of the Greed Sphere, though, he becomes increasingly paranoid, to the point where he assumes any random person who he doesn't control directly to be an enemy.
Meanwhile, deep in the middle of a twisted, evil swamp, there might be a small patch of solid ground and life created by the influence of an elven hermit who was once a great wizard who focused on Life and Earth Spheres.
Perhaps wizards could retire (like the above hermit) and, maybe, could be persuaded to come out of retirement by an adventurer.
In the above example, such a persuasive adventurer might indirectly lead to the obliteration of the swamp altogether and, if people then moved in to aid the recently-unretired wizard, a whole new civilization could form eventually.
A powerful necromancer who dedicates himself to evil and death might cause the opposite; trees becoming dead looking and, in extreme cases, gaining a malevolent sort of sentience, the dead- buried or otherwise- rising to serve him, and a general feeling of pure terror and dread.
Of course, depending on the wizard, they might choose to intentionally avoiding such things, either to keep a lower profile (Nothing says 'Oh look a pyromancer' like a huge swath of land that's partially turned to lava and is dotted by volcanoes.) or simply out of some desire for the area to remain as it is. Or something.
As for the alignments I brought up, there will most likely still be spheres related to them- areas that encourage malice or benevolence in their inhabitants, gods who demand such behavior from their followers, wizards who... well, you get the idea, right?
Maybe a somewhat kinder necromancer than the above example might instead decide to move into a town (with their permission- no matter what way you cut it, skeletal laborers and guards would put many people off the idea of letting him in.) and raise their dead as guardians to defend them.
Just my two copper coins...
Well, one copper coin. I have far too many conflicting ideas.