  We propose to correlate transmittance maps and spectral-density maps of
planar junctions, in order to analyze quantitatively and in detail
spin-dependent transport calculations. Since spectral-density maps can be
resolved with respect to atom, angular momentum, and spin, the resulting
correlation coefficients reveal unequivocally, e.g., which layers or which
orbitals determine the tunnel conductances. Our method can be used for
transport calculations within the Landauer-B\"uttiker formalism. Its properties
and features will be discussed by means of a pure bcc Fe(001) lead as well as
an extensively studied Fe(001)/MgO/Fe(001) planar tunnel junction.
