In this paper, we investigate the relation between a q-matroid and its
associated matroid called the projectivization matroid. The latter arises by
projectivizing the groundspace of the q-matroid, and considering the
projective space as the groundset of the associated matroid, on which is
defined a rank function compatible with that of the q-matroid. We show that
the projectivization map is a functor from categories of q-matroids to
categories of matroids. This relation is used to prove new results about maps
of q-matroids. Furthermore, we show the characteristic polynomial of a
q-matroid is equal to that of the projectivization matroid, which we use to
establish a recursive formula for the characteristic polynomial of a
q-matroid in terms of the characteristic polynomial of its minors. Finally we
use the projectivization matroid to prove a q-analogue of the critical
theorem in terms of Fqm​-linear rank metric codes and
q-matroids