Aitoff projection, in Galactic longitude and latitude coordinates, of the background sources of the observational sample of HI and H₂ deduced from absorption studies and used in this work (see Appendix A and Table A.1). The colorcode indicates the distance of the source. All unknown distances correspond to extragalactic sources (see Table A.1): these are arbitrarily set to 1 Mpc and indicated with black points.