Fig. 5. The spiral arm pattern used for the analysis. The arms are labelled 1 (Carina), 2 (Crux), 3 (Norma), and 4 (3-kpc). The CO emission (Paper I; Grabelsky et al. 1987) integrated in latitude from to is represented in gray-scale. Lowest contour level is at 3 . The scale in the inset figure is in kpc, and the galactic center is labelled G.C.