As indicated, the usual minimum for the width of an Orbital is about a thousand kilometres (two thousand if you count the sloped, mostly transparent retaining walls, which usually extend to five hundred kilometres or so above the plate land-sea surface). The normal ratio of land to sea is 1:3, so that on each Plate - assuming they are being constructed in the balanced pairs described above - a (very) roughly square island rests in the middle of a sea, with approximately two hundred and fifty kilometres from the shore of the land mass to the retaining walls. Orbitals, though, like everything else in the Culture, vary enormously.
- A Few Notes On The Culture