Histogram of oriented gradient (HRO) plots for two example regions, IRAS 23151 (top) and G75.78 (bottom). The X-axis shows the Stokes I intensity, and the Y-axis the projected Rayleigh statistic Z_x (also known as V). Positive Z_x values correspond to largely parallel orientation and negative Z_x to largely perpendicular orientations between magnetic field and gas column density. The dashed lines at ~12.871 correspond to 3σ significance in circular statistics.