All the information in this section is automatically known by anyone with at least one rank in Knowledge (the planes).
All planes have some degree of overlap with all other planes, but the greatest degree of overlap is between the mortal plane and the elemental planes, and between all planes and the astral plane, in which they all float.
Planes are not necessarily homogeneous. If there is an area of some foreign substance in a plane, that is generally considered to be a region of overlap between the planes – for example, the oceans of the mortal plane are simply a manifestation of the overlap between the mortal plane and the plane of water.
The planes tend to be largely finite but non-Euclidean.