N(H) distributions for each region shown in Fig. 1. The combined N(H) distribution for all regions is shown in gray. The dashed curves show the best-fit slope assuming a power-law distribution of N(H); each value for the slope is listed (see Table 1 for slope errors). Here we show PDF data of bins containing more than 10 pixels, and each major tick mark represents a factor of 10. Mean-normalization, N(H) / ⟨ N(H) ⟩ in each region, has no effect on the derived PDF slopes because the operation simply results in a linear translation of the x-axis.