Normalized histogram of V distribution across 10^° × 10^° × 1.29-km s⁻¹ tiles for ¹²CO(1–0) (top), corresponding to values presented in the left-hand panel of Fig. 2, and HI, corresponding to Figure A.3 in Soler et al. (2022). The dashed vertical line marks V = 0, which corresponds to no preferential orientation either parallel or perpendicular to the Galactic plane. The dotted vertical lines indicate V = ±2.87, which correspond to the 3σ significance levels for preferential orientation parallel or perpendicular to the Galactic plane, respectively.