Projected Rayleigh statistic V calculated from Hessian analysis of the THOR-HI and GALFA-HI observations using a 120′′ FWHM derivative kernel. Each point corresponds to a 2° × 2° × 1.5 km s⁻¹ velocity-channel tile fully covered by both surveys. The vertical and horizontal dotted lines indicate |V | = 3, which roughly corresponds to a 3-σ confidence level in the estimation of a preferential orientation of 0° or 90°. The difference in the range of V is the result of the larger significance obtained with the higher-resolution observations.