a) Hardness ratio versus log N_H for the XXL-N (blue points) and XXL-S (orange points); the hardness ratio is in good agreement with the estimated log N_H from the X-ray spectra. b) log N_H for four hardness ratio bins. The normalised dashed histograms represent the observed values in the XXL-N (blue) and XXL-S (orange) and the combined XXL-1000-AGN sample (solid black histogram). The solid lines show the combined log N_H PDF of the sources in each bin (see Appendix B for the tabulated values of these curves).