What's the actual structure/shape of Cocoon?

So far I've finished the first four or five chapters of the game. The Datalog tries to explain the setting as well as other facts while you experience the game.

However, so far I still can't really associate the locations I've explored so far to any particular structure of Cocoon. It's obviously a floating sphere/world, surrounded by clouds:

What's the structure of Cocoon? Are people living on the outside of the sphere? Do they live inside (hollow world)? If so, where's the center of mass/gravity?

The following paragraphs will reveal some minor parts of the story (first few chapters), don't continue reading if you want to experience it first.

During the first few minutes of the game, the train is seen entering a giant cave system, called The Hanging Edge (according to the Datalog it's "located near Cocoon's Outer Rim"). Where is that supposed to be? Is that on the corner of the crack(?) seen in Cocoon's depiction?

There's a big dark below the bridges and the characters speak of the land Pulse being down there, below.

However, a bit later it's revealed that down there(?) is a giant ocean which is transformed into crystal. The protagonists enter some kind of ruined city and finally manage to escape with a glider.

After travelling through clouds they'll crash land in The Vile Peaks:

According to the Datalog:

The Vile Peaks are built of debris - the castoffs of material originally lifted up from Pulse by the fal'Cie and used in the construction of Cocoon and later additions of landmass.

So where is that supposed to be? Is this still on/in Cocoon? Somewhere on the outside? Inside? In one video sequence they look up into the stars and see a floating station or city.

What's even more confusing for me are the cities visited/depicted so far, which all clearly have a clear sky, for example Bodhum:

Is Bodhum supposed to be on the outer shell of Cocoon? If so, how about the gravity? After all, Cocoon is depicted as a sphere with water dripping off/outside it (see picture above).

If possible, try to avoid spoilers in your answers, especially if this confusion regarding the structure/shape of the world is somehow meant to be experienced as part of the story (i.e. protagonists aren't sure either).