There are a couple of ways and reasons to use a book map (a bird's eye view of your book).
The first one is helpful when revising/editing to see if you have any plot holes or ways to improve the story or characters. The second is an outline in a sense. You can put plot points under each Act of the story and even keep story beats in mind as you do. While working on book 2 of the Divine Witches duology I made a book map like this to help me see each POV (point of view) and the timeline of the story. I wanted to make sure it made sense and followed the right story structure with both POVs.
I'm sharing my book mapping templates with you. I've put in a few examples to help you see how you can use them Please make a copy so you can then change things without changing my document. Also, feel free to just use this as inspiration and make your own book map the way you need it. If you have any questions please feel free to contact me at email@example.com or on Instagram @jjotisauthor.