  This paper characterizes the radial structure of stellar population
properties of galaxies in the nearby universe, based on 300 galaxies from the
CALIFA survey. The sample covers a wide range of Hubble types, and galaxy
stellar mass. We apply the spectral synthesis techniques to recover the stellar
mass surface density, stellar extinction, light and mass-weighted ages, and
mass-weighted metallicity, for each spatial resolution element in our target
galaxies. To study mean trends with overall galaxy properties, the individual
radial profiles are stacked in seven bins of galaxy morphology. We confirm that
more massive galaxies are more compact, older, more metal rich, and less
reddened by dust. Additionally, we find that these trends are preserved
spatially with the radial distance to the nucleus. Deviations from these
relations appear correlated with Hubble type: earlier types are more compact,
older, and more metal rich for a given mass, which evidences that quenching is
related to morphology, but not driven by mass. Negative gradients of ages are
consistent with an inside-out growth of galaxies, with the largest ages
gradients in Sb-Sbc galaxies. Further, the mean stellar ages of disks and
bulges are correlated, with disks covering a wider range of ages, and late type
spirals hosting younger disks. The gradients in stellar mass surface density
depend mostly on stellar mass, in the sense that more massive galaxies are more
centrally concentrated. There is a secondary correlation in the sense that at
the same mass early type galaxies have steeper gradients. We find mildly
negative metallicity gradients, shallower than predicted from models of galaxy
evolution in isolation. The largest gradients occur in Sb galaxies. Overall we
conclude that quenching processes act in manners that are independent of mass,
while metallicity and galaxy structure are influenced by mass-dependent
processes.
