Same as Fig. 8, but overplotted with diagnostics to illustrate potential issues in the distance assignment. The position of the Sun and the Galactic centre are indicated with a Sun symbol and a white dot, respectively. Solid white curves show constant projected v_LSR velocities. The dashed white curve marks the locus of tangent points and dotted lines indicate the area where v_LSR values are within 10 km s⁻¹ of the tangent point velocity. Shaded areas show GRS regions that either had limited latitude or velocity coverage. The yellow dashed ellipse indicates a likely artefact of nearby emission that was erroneously placed at far distances. See Sect. 4.8 for more details.