OH column density vs. the column density of H I (left), H₂ (middle), and the column density of the total number of hydrogen nuclei (right). Features associated with line-of-sight absorption are shown in blue, features associated with H II regions in black (Rugel et al. 2018). The middle panel shows N_OH vs. N_H2. Lower limits in case of saturated H I absorption in the left and right plots are indicated by triangles pointing to the right. There is one upper limit due to the non-detection of CO, which is indicated by triangles pointing to the left. Typical error bars are indicated in the lower right corner. The limit of a 3σ detection is indicated by a dashed gray line. The green dashed line indicates the fit of a correlation to the data.