Left panel: longitude–velocity diagram for the Gaia HQ DIB λ862 sample. The circles indicate the median V_LSR and standard uncertainty of the mean for each field. Velocity curves calculated by Model A5 in Reid et al. (2019) for different galactocentric distances (R_GC) are overplotted. Right panel: same as left panel but superimposed on the ¹²CO data from Dame et al. (2001). The colour-scale displays the ¹²CO brightness temperature in a logarithmic scale integrated over the velocity range.