My game is going to be set in the San Francisco Bay Area, and I plan to feature ley lines in the setting. The first thing that came to mind was the San Andreas Fault, which seems like a natural to be connected to an Earth Line. But to make it more interesting, I remembered that the S.A. Fault is part of the tectonic/volcanic system known as the Ring of Fire (how's that for an evocative name) which surrounds the Pacific Ocean.
So, now I'm imagining a network of interwoven Earth and Fire lines which follow the major faults and volcanic chains around the Pacific Basin. Their fluctuating power and interactions mean that their associated Nexuses tend to shift locations (although the more potent, such as volcanoes are relatively stationary), and occasionally bleed into the surrounding landscape as earthquakes. I will note here that, in San Francisco at least, a strong connection between Earth and Fire can easily exist; the Quake of 1906 was followed immediately by the Fire of '06, which burned down most of the City and left thousands homeless.
An opposing system of Water Lines feeding into the Bay along the major rivers and flowing out into the Pacific under the Golden Gate, will cross the Ring of Fire Lines at roughly right angles, and could create some interesting effects where they intersect. I may have Air Lines moving in tandem with Water, though they won't be as strongly connected as Earth and Fire (although the famous S.F. fog comes to mind here). I also imagine that there will be some strong Spirit Lines as well, and as I'm going with an "opposing forces" theme, they will likely be a mix of Light and Dark.
