Mapping out is not a term Ive heard for this particular idea ( seeing past lives) but I have heard the term used in other ways when it comes to reincarnation, life etc.
But the conceot I think Kelvys getting to, is the ability to view your past lives, or at least moments of them. Of course, you have to believe in the possibilities of past lives in order to try it.
What I do is kind of like meditating. I get comfy, relax, get all the mundane things out of my head and try ot have an open, clear mind. I close my eyes and just try to be an open book. Once I'm at that point, I picture a path running through woods with paths on either end. Each one metaphorically leads to a life you have lived. You pick a "path", walk to the end, and when you're out of the "woods" you are now in a moment of one of your lives. I usually see through my own eyes and everything is fairly vivid, from color to texture, smells, sounds, touch, etc.
Everyone has their own technique of doing this, and for some it comes easier than others. But practicing it makes it happen more smoothly and swiftly