In Ubuntu I can partition a HD (to be entirely used for Ubuntu) before I install. The installer sees the partitions and installs into them rather than into its singular [default] "OS" partition.

That is particularly slick because the install process remains automated, rather than interactively slow and more open to typos during an interactive full-install.

Some advantages of this 'modular' partitioning of '/':
1) my /var/ folder can have its own partition so that I can have a database installed and developed in there; if I have to re-install Ubuntu, that process will preserve my database.
2) my /home/ with all of its users' .-files and specifics will not be lost.
3) all of my locally-installed (downloaded, installed, licensed, and configured) local tools will remain safe.
4) I can backup single partitions on a schedule based up the access to and use of that partition's content.

So, I'm looking at Fedora and am uncertain if the same pre-partitioning is viewed by the installer?

Restating, can I partition before a Fedora installation, or, does the install just give a 'choice' between me either accepting its default partitions or doing my partitioning through the installer's interactive steps?

Thanks,
"frank"

Do you mean have anaconda (the installer) somehow automatically recognise each partition and assign to an appropriate mount-point ?. No, that ain't going to happen on a normal (non-kickstart) install.
At the partitioning stage you can assign partitions to mount points and whether to format them or not. These will be honoured during the install. Been a very long time since I did a Ubuntu install, but I imagine it's similar.

Just noticed this is a duplicate - reported for closure.