Ley lines are typically healthy, making Seelies' and warlocks' magic function well on a day-to-day basis. However, they have been proven to be corruptible, but it takes extremely powerful magic to pull off.
For protective reasons, against rare but dangerous instances such as ley line corruption, the New York Institute is not built on any ley lines. Meanwhile, the site of the Church of Talto is one where the ley line concentration gives off plenty of energy.
- At one point, Jocelyn Fray used New York's ley lines as a map to a location—a park she used to bring her young daughter to, where ley lines intersect—where she hid a mirror meant to mislead anyone looking for the real Mortal Mirror.