The answer is a storyboard!
Storyboards are used in the film and TV industries and usually have three components: the narration (the manuscript), the sketch that shows what’s happening when that narration is heard, and the directives. Now, directives are an important distinction from a storyboard made for a book, because in movies and TV, there is the element of movement. So within the directives, you write out how the scene “comes onto” the screen, how it transitions to the next scene, you describe any movement occurring, any special effects; basically, you include anything visual that is happening during this chunk of narration.
You’ll recall that I’ve made dummies of my books before. This is another approach to mapping out the story arc for a book. The dummy helps to figure out the pacing for the text, since you make a small version of a book with pages. As you read through the text on each page, and turn the page to find out what happens next (just as a reader of your book would do), you see how the story unfolds across the entire span of the book. Is your action too bunched up within the 32 pages, such that only 4 pages are interesting while the rest feels like filler? Does your exposition (introduction of setting, characters and “the problem”) take up too many pages so that getting to the action would challenge even your attention span? Can you space out the action to create even more suspense? Try it out, you’d be amazed at how helpful a tool this is!