Distance along the Z axis of the majority of the dust mass (see text for a definition). Distances are in parsecs and positive towards the northern pole. In the third quadrant, most of the dust is below the mid-plane (but see text), while it is the opposite in the second and fourth quadrants. Also shown are the projections onto the mid-plane of the boundaries of the thick vertical slices from Fig. 13, numbered from 1 to 4.