Longitude‐velocity map of the SiO detected sources overlaid on the CO l‐v map (left), (taken from Bania 1977) and the linear fits for three groups with different distances (right). The left panel illustrates the empty area of SiO (﹩l=-0\fdg 4﹩–1 and ﹩V_{\mathrm{lsr}\,}=20﹩–150 km s⁻¹). The circles, squares, and the triangles in the right panel indicate the sources with distances in 5–7.5 kpc, 7.5–9.5 kpc, and above 9.5 kpc, respectively. The best fit to the three groups are shown in the thin, dashed, and dotted lines.