Spatial correlation between the four different tracers across velocity channels as evaluated using the histogram of oriented gradients method (HOG; Soler et al. 2019). The figure shows all tracers correlated with each other as labeled at each plot. The panels show the values of the projected Rayleigh statistic (V), a measure of the morphological correlation between velocity channels. A high value of V indicates a strong correlation between the corresponding velocity-channel maps. The contours correspond to the 7σ confidence limit on the V values (see Soler et al. 2019 for more details).