Ah, as for source I use this. Druids are clearly apart in regards to that:
<explanation, system specific>
Druids gain their magics from the Divine, the Gods of Nature. A Druid is a kind of a Priest, not something else! He is NOT drawing power from the land, but from the divine essence that reside within his lands. In my setting that essence is clearly different from the essence of the stones and the trees, the earth and the air. There are other priests as well; Bishops, Ceremony Masters, Reverends, Mullahs, etc... based on the religion and location.
A Mage/Witch/Warlock/Witchdoctor/etc is a mage, using whatever spells he has at his disposal. His magics come from rift channelling, the manipulation of essences* through the use of incantations, gestures, dances, ceremonies, foci, songs, blood and so on. The different titles indicate gender, powerlevel, rulership and field of specialty. There are drastic changes from a Warlock to a witch of the Shievren.
</explanation, system specific>
Then there are the Shamans. I agree with Rupert: They are largely unsuitable for play. The reason might be their unique ties to their location but also their social role. Shaman Priests might have been playable, if I were to have an "evil type group", but I learnt to avoid that long ago.
A strong connection to the "home turf" is a cool idea, but also one that makes Shaman characters even less desirable to play. I much prefer your "inherited local powers" AND retaining the ability to perform magics, albeit not world rattling ones, outside the home territory.
*The 6 essences are the 4 elements + black essence(that which tear apart and kills) and white essence(that which keep together and creates life)
Why the Shaman is stronger at home:
As the Shaman utilize his magic, he draws upon the power of the surroundings. If he is to make his skin hard, he calls to the stones, asking for their "Mekhros" (my term) to protect him and steel his skin against harm.
At home the spirits of the earth and the stones* know him. They are his friends. If he calls to an oak, the oak readily help him, even go out of its way to boost his magic. When the Shaman needs an animal companion, the entire forest might answer his call, so he better be careful to specify who he wants.
When he is away this changes. He is still able to contact the forest and earth spirits, and the animal souls. But now the rules have changed. To them he is a stranger, might even be an intruder. He has either got to force them to co-operate, which will alienate them in the future, or he has to convince them.
A logical continuation of this is that the older an area is, the more ancient and powerful, rich on animal and spirit life, the more power will be available to the Shaman of Nature. So if the Shaman and his ancestors have lived in the area a long time, their magics will be powerful indeed.
Edit: Removed some gibberish.