Face-on view of the Galactic inner disc with the four-arm spiral pattern of Steiman-Cameron et al. (2010) overlaid on top. The Sun is at coordinates (x,y) = (0,−8,3) kpc. The disc rotates clockwise and the approaching (QIV) and the receding (QI) sides are shaded in blue and in red, respectively. An indicative 3-kpc bar is shown, oriented at 30° with respect to the l = 0° sight-line (Wegg et al. 2015). The three circles (grey dotted lines) show the radii of the gas overdensities discussed in the text, while the red and blue dashed lines show the sight-lines that are tangent to these circles. The gas overdensities at R = 4.5,6.4 kpc are consistent with the sight-lines intercepting the spiral arms.