Many years ago, I was showing a friend my new between-the-wall-studs bookshelves for paperbacks; I gestured to different areas, pointing out that over there were biographies, and here were science fiction classics, and up there were novels by my favorite authors. He pointed to a shelf where I happened to have two copies of James Gleick’s Chaos, and said “This must be your lifestyle section.”
Years later, in a different house, I used the same strategy, with slightly classier woodwork. I came home one day to find my housekeeper had emptied the shelves, washed them, dusted the books, and shelved the books in an order I couldn’t identify. I asked. She had organized them according the dominant color on the spines.