Geometry vs Geometries

Geometries is a quite common term in CAD..

Yes, I understand that. CAD and its common terms aside though; which would be grammatically correct? Or, is it that neither are incorrect, so it's more of a "dealers choice" situation? lol

Their use is not a matter of choice but of context.

Oakie Doakie... : "There is a virtual metric-sh#t-ton of geometr(y/ies) in here. The total amount is comprised of individual pieces, each of which is a mere .05-metric-sh#t-GRAM. I have selected an excessive amount... Just LOOK at all the *geometr(y/ies)* that (is/are) now selected!... LOOK AT THEM!!!!"

So, in this context, which one do ya pick?

In this context you should use the plural.