Legacy of War
In the centre is the Prime Material Plane surrounded by an Ethereal plane (misty realms of proto-matter). Outside of the Prime and Ethereal is the Inner planes, also called the Elemental planes, which each have their own structure based on a sphere. Then comes the Astral plane which connects the Prime Material plane to the last sphere, the Outer planes.
The Outer planes, also called the Planes of Power, are 16 planes arranged in a circle (the Great Wheel) defined mainly by alignment and surrounding a 17th neutral plane known as Concordant Opposition.
These seventeen outer planes:
Hades/The Gray Waste
Happy Hunting Grounds/Beastlands
The Nine Hells/Baator
Seven Heavens/Mount Celestia
The Inner planes are the six major elemental planes (Fire, Earth, Water, Air, Positive Energy, Negative Energy), the four para-elemental planes (Smoke, Ice, Ooze, Magma), and the eight quasi-elemental planes (Lightning, Steam, Radiance, Minerals, Vacuum, Salt, Ash, Dust). They can be thought of as being on the surface of a sphere with Positive Energy at the north pole, Negative Energy at the south pole and Fire, Earth, Water, and Air on the equator, equidistant from each other. The para-elemental planes are found on the equator between the boundaries of Fire, Earth, Water and Air (Magma is between Fire and Earth, for example). Four of the quasi-elemental planes are found between the boundaries of Positive Energy and the four elements (Steam was between Positive Energy and Water, for example). And the other four quasi-elemental planes are between Negative Energy and the four elements (Vacuum is between Negative Energy and Air, for example). The Inner planes are surrounded by the Ethereal planes, which connected them to the Prime Material plane.
Demi-planes, are planes of finite extent found within an Ethereal plane. They may have been the creations of extremely powerful wizards, technologists, or deities or they may have been created when a large glob of proto-matter began to pull away from its Ethereal plane and achieved separation. Demi-planes might eventually collapse in on themselves, re-merge with its parent Ethereal, or merge with an Inner plane or Prime Material plane. Each demi-plane had its own rules regarding gravity, vision, magic, and material make-up.
The Prime Material Plane touches both the Astral plane and its Ethereal plane. It consists of all known worlds as separate continents: Catti, the Forgotten Realms, Greyhawk, Eberron, Kalatar and Dragonlance.
Note: This set up uses the Planescape rules which merge all material planes into one plane which while “earth-like” is also nearly infinite in nature, including all known and some unknown pre-existing planes. The other popular option is the Realmscape rules, which have multiple Material Planes, one for each world. In which Catti would be a plane in itself, consisting of Daeland and any other locations presented in the Legacy of War that does not already belong in another setting. The reason I have chosen to use the Planescape rules is so events that happen across the world will have a bigger impact on the rest of the world and players who play in more than one campaign will enjoy seeing the effects of their previous characters’ actions.