TITLE: Minimal size of an open affine cover
QUESTION [7 upvotes]: This may be a silly question - but are there interesting results about the invariant: the minimal size of an open affine cover? For example, can it be expressed in a nice way? Maybe under some additional hypotheses?

REPLY [3 votes]: I think there are some relevant comments in the work of Roth and Vakil, The affine stratification number and the moduli space of curves.