Orphans of the Sky by Robert A. Heinlein

The mutants are described as living nearer to the external hull of the ship. This understanding of the basic geometry of the Vanguard is at odds with some other considerations and events described in the book.

That implies that humans live on the outermost decks (cylinders) while the mutants dwell in the innermost decks (cylinders). So, one would think that going 'up' on the Vanguard means moving towards the central axis of the ship and that the geometry of the various decks consists in being concentrical cylinders, all having a common axis. It is quite clear that in order to have a gravitational field in a ship travelling inertially in outer space you need to have the ship (or part of it) rotate around an axis, but as you get closer to the axis the gravity gets weaker, e.g. The command center of the Vanguard-long forgotten to the humans- where the main character Hugh eventually can 'see the stars' is in what seems to be the uppermost deck. The humans live in the lower decks where the gravity level is normal, while the mutants live in the upper decks, where the gravity is weaker and the more weaker as one climbs up.

The ship is described as a huge cylinder with many layered decks. I have a question regarding the structure of the spaceship Vanguard featured in Heinlein's 1941 novel Orphans of the Sky (Wikipedia' synopsys here).

Orphans of the Sky by Robert A. Heinlein