in the Languages of the Night, a collection of Ursula K. LeGuin's essays on writing, there is a section(IIRC I read it more than 20 years ago) where a famous fantasy magazine editor had asked her to go into how she mapped out her world and created all the documentation beforehand so she could refer to it when needed, her process as it were, and she replied something to the effect of this is not how I do it.
The description of how she did it was that when it became time to have that information, she looked it up in her mind and it came to her, what we might describe as making it up as she went along but which was more like querying her unconscious knowledge of the places and people she was describing.