The newest editions of Choose Your Own Adventure books come with maps of the story structure that depicts all the branches, endings, and links of each story.

On the official maps, however, the endings aren’t coded in any way that reveals their nature. Instead, they operate according to a simple key: each arrow represents a page, each circle a choice, and each square an ending. Dotted lines show where branches link to one another.

Mapping the bones of the books can have other purposes, too. Nick Montfort, a poet and professor at the Massachusetts Institute of Technology who studies interactive fiction, has a habit of asking people what they know about “Choose Your Own Adventure” books. “They often say, ‘You have two choices after every page,’” he says. “That’s not true. Sometimes you have one choice. Sometimes you have more than two. When you show the maps, you can see that these books don’t look exactly the same.”