I should also mention that Underdark, another Forgotten Realms title, describes 'Earth Nodes', places of power where spellcasting is enhanced. There are feats related to such nodes in the book, to enable characters to tap the power.
Also, the 2nd Edition Birthright rules had a Domain Spell casting system (spells that affected a whole region) which were tied to networks of Ley Lines and Sources (nodes of magical power). The Book of Magecraft (available as an ESD I believe) had some notes for optional rules. Sources also could enhance magic when cast at their location, and there were specific spells and magic items that allowed you to work with Ley Lines and Sources.
Also, the 2nd Edition Birthright rules had a Domain Spell casting system (spells that affected a whole region) which were tied to networks of Ley Lines and Sources (nodes of magical power). The Book of Magecraft (available as an ESD I believe) had some notes for optional rules. Sources also could enhance magic when cast at their location, and there were specific spells and magic items that allowed you to work with Ley Lines and Sources.
