  3D spectroscopy produces hundreds of spectra from which maps of the
characteristics of stellar populations (age-metallicity) and internal
kinematics of galaxies can be derived. We carried on simulations to assess the
reliability of inversion methods and to define the requirements for future
observations. We quantify the biases and show that to minimize the errors on
the kinematics, age and metallicity (in a given observing time) the size of the
spatial elements and the spectral dispersion should be chosen to obtain an
instrumental velocity dispersion comparable to the physical dispersion.
