Column density N_H of the X-ray absorbing material as a function of distance from the Sun in the solar neighborhood. Top panel: differential N_H. Bottom panel: cumulative N_H for the same measurements as in the top panel (solid lines). The dashed lines and hatched regions around them show the N_H value with its uncertainty, as retrieved from the HI4PI survey in the same directions as indicated by the labeled colors in the top panel (see also the empty white squares in the chart map of Fig. 6).