Cosmology

Cosmology is the study of the nature of the universe. Physical cosmology is the physics of its origins and evolution; religious or mythological cosmology is a body of beliefs based on mythological, religious and esoteric literature, traditions of creation and eschatology. Worldbuilding borrows the word: constructed worlds "often have cosmologies, both in the scientific and metaphysical senses of the word". A fictional universe's cosmology is its invented origin and structure, the heavens, planes and creation myth beneath the fantasy map.

For the writer it is the frame under the world: where the gods live, where the dead go, which planes touch the world. A craft guide asks: "How is the world put together, what is the afterlife like", because a setting's cosmology "can be a very big deal in a fantasy setting, and drive all sorts of plots". Fix it before chapter one: cosmology binds the mythology, the belief systems of how to create fictional religions and every worldbuilding layer above it.