N-PDF of the Draco region. The black histogram shows the N-PDF obtained from Herschel data and the blue line its analytic description. The red line is the result from fitting two log-normal PDFs and considering the noise contribution that leads to a linear behavior at low column densities (Ossenkopf et al. 2016). The green histogram displays the N_HI-PDF of the H i data and the continuous line a single log-normal fit. The fitted peak positions of the PDFs and the widths (σ in units of η = ln(N/〈N〈)) are given in the panel. Error bars are based on Poisson statistics. The left y-axis gives the probability density for the Herschel map and the right y-axis for the H i map.