[CentOS] C 7, docker, and storage

I may have missed some overnight replies to my question from yesterday -
if so, sorry.

>From my googling, it looks like I should change from the loopback device
to overlayFS (with overlay2). What I haven't found is, first and foremost,
more clarity on configuring storage.

It *appears* that the loopback storage is just a directory under
/var/lib/docker (yet I see a reference in someone's blog to ~docker - *is*
/var/lib/docker intended as ~docker?

Can I make a docker directory elsewhere, on another filesystem that has a
lot of space, and configure docker to use that, or do I need to symlink
from /var/lib/docker to the new place? And should I move all the old stuff
under /var/lib/docker to the new location (of course have shut down
docker)?

        mark