Double logarithmic plot displaying N_HI versus optical extinction A_V for central sight lines. The optical extinction is calculated with R(V) = 3.1 (Gordon et al. 2003) and applying correction factor from Schlafly & Finkbeiner (2011) to the SFD data. N_HI is determined from HI4PI. The dots and crosses represent H I absorption detections and non-detections, respectively. To guide the eye, the dashed line representing the best fit gas-to-dust ratio (Eq. (6)) is plotted in the left panel. The color coding represents the peak H I optical depth (tau_max_val; left panel) and the absolute value of Galactic latitude (Peak_pos_b; right panel).