Results of the HOG analysis of the THOR HI and GRS ¹³CO observations. Left panel: projected Rayleigh statistic, V (v_13CO, v_HI), the HOG statistical test of spatial correlation between HI and ¹³CO velocity-channel maps, defined in Eq. (3). The contours indicate the 3ς_V, 4ς_V, and 5ς_V levels in the corresponding velocity range. Right panel: mean resultant vector length, r(v_13CO, v_HI), with the 3ς_V confidence interval, a HOG metric that is roughly equivalent to the percentage of gradient pairs that imply the spatial correlation between the velocity-channel maps, defined in Eq. (2).