Ley Lines, Nexus Points, and Gates:
It is said that the ley lines have always always been there, and were used by spellcasters for the benefits they provided (a particularly powerful effect when at a nexus point, I’m told). The lines now to burn a brilliant red (although they aren’t actually on fire), but I’ve read that they used to be a soft blue prior to the cataclysm.
Ley energy adds power to arcane and divine spells, as well as spell like and supernatural abilities. When near a Ley line (roughly 500’), a caster may either increase the DC by 1, or increase his caster level by 1. When within 30’ of a ley line, or roughly 500’ from a nexus point, this bonus increases to 2. When within 30’ of a nexus point, this bonus increases to +3.
However, the energy drawn from a nexus point when casting spells close them seems to have a destabilizing effect which can lead to the opening of a gate. Higher level spells and proximity to the gate seem to increase these chances exponentially.