Maximum gas density n_H along the lines of sight parallel to the X axis within the selected clump. Contours show the total gas column density N_H from 3 × 10²¹ cm^-2 to 1.1 × 10²² cm^-2 in steps of 10²¹ cm^-2. The “clump” displayed here has a size roughly 1.5   pc    ×    2.5   pc. The two-dimensional slab of gas under study is seen projected as the single-pixel-wide AB strip. The white triangle marks the position of the maximum value of max(n_H) in this region, and the white circle that of the maximum of N_H. They are separated by 0.65 pc.