Projected Rayleigh statistic (V) corresponding to the orientation of the filamentary structures identified in the 2° × 2° tiles and across velocity channels in the THOR HI and MWISP ¹²CO and ¹³CO observations. The overlaid curves correspond to selected spiral arms from the model presented in Reid et al. (2016). The plus sign (+) and the cross (×) mark the tiles with the highest and the lowest V, respectively, whose maps are shown for reference in Fig. 2. The star symbols mark the positions of the SN remnant W44.