We investigate factor maps of
higher-dimensional subshifts of finite type. In particular, we are interested in how the
number of ergodic measures of maximal entropy behaves under such factor maps. We
show that this number is preserved under almost invertible maps, but not
in general under finite to one factor maps. One of our tools, which is of
independent interest, is a higher-dimensional characterization of entropy-preserving
factor maps that extends the well-known one-dimensional characterization
result.