Ley lines are the provinces of the fey.
Ley lines are used by Downworlders to create entrances into the Faerie, among others. Faeries in particular use them often. Though invisible, one can be trained to sense ley lines. The Adamant Citadel is said to be built on ley lines—this granted the faeries and their Dark War ally access to the typically remote location.
There are points, also called sacred sites, where ley lines meet, or "converge", forming a matrix within which magic is amplified, particularly ones that has to do with magic transferrals. It is where every ley line in a specific area link up. Meanwhile, two ley lines that cross are collectively called "junctions". Junctions are also considerably powerful places, but less so than convergences. The altar of Porthallow Church was built at a junction.
- The term ley lines and its use in The Shadowhunter Chronicles most likely refers to the concept usually associated with Celtic folklore: the spiritual and mystical alignments of land forms, similar to a spirit or fairy path—a route taken by fairies usually in a straight line and between sites of traditional significance.