Hello, newbie here.

I've been trying to teach myself animation for about 6 months. I've hit something I'm completely stumped by, and wondered if anyone could help?

I'm trying to do a 360 head rotation, along the lines of these:

https://www.youtube.com/watch?v=60WJpCww8Dk
https://www.youtube.com/watch?v=dewuJqCK3xM

I get the general gist of it and can do a rough freehand rotation. The thing I'm interested in is the circle projected on to the square underneath, used as a guideline, and how exactly they're using it. And I'm baffled about what the rule is for the pivot point for the character. In some it seems like the base of the skull and some it seems like the top of the spine.

I don't really know what this head rotation or turnaround grid thing is called so I don't even know how to search for this thing on google. Any ideas?

Thanks.