  Methods to recover the fossil record of galaxy evolution encoded in their
optical spectra have been instrumental in processing the avalanche of data from
mega-surveys along the last decade, effectively transforming observed spectra
onto a long and rich list of physical properties: from stellar masses and mean
ages to full star formation histories. This promoted progress in our
understanding of galaxies as a whole. Yet, the lack of spatial resolution
introduces undesirable aperture effects, and hampers advances on the internal
physics of galaxies. This is now changing with 3D surveys. The mapping of
stellar populations in data-cubes allows us to figure what comes from where,
unscrambling information previously available only in integrated form. This
contribution uses our starlight-based analysis of 300 CALIFA galaxies to
illustrate the power of spectral synthesis applied to data-cubes. The selected
results highlighted here include: (a) The evolution of the mass-metallicity and
mass-density-metallicity relations, as traced by the mean stellar metallicity.
(b) A comparison of star formation rates obtained from H{\alpha} to those
derived from full spectral fits. (c) The relation between star formation rate
and dust optical depth within galaxies, which turns out to mimic the
Schmidt-Kennicutt law. (d) PCA tomography experiments.
