The Hydra system, the birthplace of the maggot-cyborgs of Hydra, existed within the Aparo sector of the Outer Rim Territories' Catarlo sector.
As noted in the StarWars.com Online Companion for The Essential Atlas reference book from 2009 by Jason Fry and Daniel Wallace, the Hydra system was situated in grid square R-3.
- The Star Wars: The Essential Atlas Online Companion on StarWars.com (article) (backup link) (First mentioned)