Just a quick overview, the Mists connect every thing to each other, and in the center of the Mists, is the Rift, the center of the universe. In the center of the Rift, is the Hall of Heroes.
We also know that the Underworld and the Realm of Torment are connected. Some believe that the Realm of Torment is a sub-section (of a sub-section) of the Underworld. I disagree. Why? Why would a sub-section of a sub-section of a realm need the word Realm in the name.
We can also assume that the Underworld is connected to the Hall of Heroes, by the order of the HA/Tomb Maps (Underworld->Scarred Earth->Courtyard->Hall of Heroes *HA maps have more*). In the Underworld map in Tombs, you can see in the background the Twin Serpents, or at least one of them.
My hypothesis is based on the general layout of the Rift, Mists, and the Realm of the Gods. I drew a basic idea of what my hypothesis is.

Please note: In my drawing, the shapes and sizes were done as such for simplicity, I am not suggesting those are the size comparisons, or the shapes, just general locations.
In the top drawing, the Realm of Torment and the Underworld would be next to each other, which would be why they are connected. The location of the other Realms of the Gods are uncertain, along with where the Underworld and Realm of Torment is located.
I believe that all the Realms of the Gods are connected to the Hall of Heroes, and all reside in the Rift. The Realm of Torment, being Abaddon's prison, was separated from the rest to prevent as much contamination by him as possible, and to serve even more as his prison.
After all, if they can pull entire buildings into different dimensions, and shift dimensions to their will, what stops them from being able to move/split up dimensions.
Also, my drawing proposes that Tyria is closest to the Underworld. This is only supported by the fact that the way to the Hall of Heroes takes us through a part of the Underworld. So this might not be the case.
In the bottom drawing, I tried to show how it would be to get to the Hall of Heroes, I am not saying that the Hall of Heroes is above the rest, like Mount Olympus is in Greek Mythology, but I wanted to show that the path to the Hall of Heroes is what separates it from the Realms. We only know the path from the Underworld to the Hall of Heroes, we know nothing of the other Realm's paths, and with so little room, I couldn't make six paths.
I also am not trying to say the Realm of Torment is underneath the rest (although that would fit the hell persona), just that it is separate from the rest. And not to mention broken up in of itself.
I am sure I am forgetting something, so sorry if I am. Also, sorry about the poor quality of the drawing (I'm not the best drawer and I have a rather old scanner, so not everything is clear to see).