Question: In [Iain M. Banks'](https://en.wikipedia.org/wiki/Iain_Banks), fairly rockin' [Culture novel](https://en.wikipedia.org/wiki/The_Culture), [*Consider Phlebas*](https://en.wikipedia.org/wiki/Consider_Phlebas) a good third of the book takes place on what is called the **"Vavatch Orbital"**. An orbital is apparently a massive artificially created megastructure, similar to the [Death Star](https://en.wikipedia.org/wiki/Death_Star) or the titular [Halo](https://en.wikipedia.org/wiki/Halo_%28megastructure%29).

At one point in the book the Vavatch Orbital is described as a minor orbital, not as big as a ring or a sphere. Then later it is almost directly described as having a ring shape. Still earlier in the story it is described as a bucket being swung in circles, though this description maybe used only to describe how the orbital uses centrifugal force instead of actual gravity.

Whatever the size, the orbital has to have enough sea space for a Megaship (a city sized ocean ship) to travel for more than a century before reaching land again.

[Wikipedia tends to suggest that all orbitals are rings](https://en.wikipedia.org/wiki/Orbital_%28The_Culture%29), but then why the mention of a sphere, or that Vavatch is not big enough to be a ring?

Answer: 
Here's how Banks describes Orbitals himself, in his essay [*A Few Notes On The Culture*](http://www.vavatch.co.uk/books/banks/cultnote.htm) :

> 
> Perhaps the easiest way to envisage an Orbital is to compare it to the idea that inspired it (this sounds better than saying; Here's where I stole it from). If you know what a Ringworld is - invented by Larry Niven; a segment of a Dyson Sphere - then just discard the shadow-squares, shrink the whole thing till it's about three million kilometres across, and place in orbit around a suitable star, tilted just off the ecliptic; spin it to produce one gravity and that gives you an automatic 24-hour day-night cycle (roughly; the Culture's day is actually a bit longer). An elliptical orbit provides seasons.
> 
> 
>
I pictured it as a HUGE ring, but ring in the sense of the thing on your finger, it orbits itself, the slow rotation causes things to fall, but doesn't generate gravity due to having limited mass (compared to a GSV or planet), the "surface" is either the inside "up" or the outside "down", I'm guessing the outside would be unlivable.

The "inside", if you will, is a huge expanse slowly curving upwards, like our planets horizon curves downwards, but as it is so vast the curvature happens outside humans fields of vision, appearing to be a flat ocean etc. Imagine a perfect skateboard ramp circle, with open ends, and possibly the width of a planet, but with nothing Inside but space & air.. (maybe not even air in the middle)..