I have been learning about Figure Drawing because I would love to learn how to draw bodies and Mapping is one of the techniques that has been the most helpful to understand how to place something on a white page.
Mapping is just selecting points as in image 1 and 2, connecting them and create a map on a white page as shown in the images below. I would recommend you just to repeat and practice and you will understand little by little more about mapping.
The materials I’ll recommend you to use are old magazines with full body poses that have more movement and Posca PC-1M or PC-1MC bullet shaped 0.7 mm.
The mapping that I created during different days was this:
I hope this is helpful for your drawing path. Let me know if you have questions.