What is it called when you display an outline version of a photograph next to the image and label or number it?

It’s usually done when there are a bunch of objects in a photograph and it’s hard to identify them or refer to a specific one without confusion.

For instance, I’ve seen this done with jigsaw puzzles that have a certain theme, and on the back, there’s an outline illustration that has numbers on it that correspond to a numbered list of elements.

I’ve seen something similar done with mountain ranges, where it’s hard for a person unfamiliar with the individual peaks to pick them out.

An example:

I feel like it’s kind of a “retro” approach, but because I don’t know the right words to describe it, I’m finding it near impossible to locate other examples.

EDIT: I just found a better example from this blog post:

They call it a key, which feels right though mostly I keep finding images of literal keys. 😉

Answer

Attribution
Source : Link , Question Author : Sarah Lewis , Answer Author : Scott