Left: Cosmic-ray ionisation rates derived from OH⁺ vs. galactocentric distance. The filled black triangles and unfilled red diamonds represent ζ_p (H) values derived from the LOS absorption features observed in this study and in Indriolo et al. (2015), respectively. The dashed black line marks the median value of the total ζ_p (H) distributions. The solid-dotted line represents the derived cosmic-ray ionisation rate gradient. Right: Histogram distributionsof ζ_p(H) derived in this work displayed in black, that from Indriolo et al. (2012) in red, and the combined distribution by the hatched grey region.