I₈₅₇ vs. N_HI scatter plots, visualising the dust-gas correlation for each of the three Hi components, across a row. The fields POL and POLNOR do not have an HVC component. For a given Hi component, the remaining 857GHz emission, once the contribution of the other two Hi components has been removed, is plotted as a function of N_HI of that component (i.e., as a function of ). The contours show quartiles of the density of points in each scatter plot. The filled contours show the data points used in the correlation analysis (i.e., data points not masked out) while the open contours show all data points.