The map was built by the combined efforts of the Silent Brothers, including Brother Zachariah, and warlocks of the Spiral Labyrinth, including Catarina Loss and Magnus Bane. The map was created for the Clave, after the Dark War, to track and detect the use of dark magic—specifically necromancy, "energy raised from evil sources, Hell dimensions and the like, to draw power and extend life," similar to the kind that Sebastian Morgenstern used.
In August 2012, Magnus and the others were alerted by least two instances of dark magic detected by the map. For the first, Magnus went to Los Angeles to to ask Malcolm Fade, and it was easily dismissed when Malcolm told him that it was just a rogue necromancer and had been handled.
The second was when Malcolm's entrance to the convergence site was destroyed, uncovering the longstanding dark magic activity and making it visible on the map. Magnus, Robert, Jace, and Clary responded to the flare-up.