Srimad Bhagavatam Canto 05, Chapter 26, Text 05

SB 5.26.5

rsir uvaca
antarala eva tri-jagatyas tu disi daksinasyam adhastad bhumer uparistac ca jalad yasyam agnisvattadayah pitr-gana disi svanam gotranam paramena samadhina satya evasisa asasana nivasanti.
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The great sage Sukadeva Gosvami answered: All the hellish planets are situated in the intermediate space between the three worlds and the Garbhodaka Ocean. They lie on the southern side of the universe, beneath Bhu-mandala, and slightly above the water of the Garbhodaka Ocean. Pitrloka is also located in this region between the Garbhodaka Ocean and the lower planetary systems. All the residents of Pitrloka, headed by Agnisvatta, meditate in great samadhi on the Supreme Personality of Godhead and always wish their families well.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
As previously explained, below our planetary system are seven lower planetary systems, the lowest of which is called Patalaloka. Beneath Patalaloka are other planets, known as Narakaloka, or the hellish planets. At the bottom of the universe lies the Garbhodaka Ocean. Therefore the hellish planets lie between Patalaloka and the Garbhodaka Ocean.
Srimad Bhagavatam Canto 05, Chapter 26, Text 04
Srimad Bhagavatam Canto 05, Chapter 26, Text 06