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 provide strong evidence of, e. g., which layers or which orbitals determine the tunnel conductances. Our method can be used for transport calculations with the Landauer-Büttiker formalisms. 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) magnetic tunnel junction.