Distributions of 572 H II regions (Sect. 4.1) with accurate distances projected onto the Galactic disc. The H II regions with parallax-based (P) distances are shown by red dots, while those with spectrophotometric (S) distances are indicated by grey dots. Also shown in the plot are the distance uncertainties (underlying line segments). The dot size is proportional to the estimated radio luminosity of the H II region at 5 GHz. The positions of the Sun and GC are the same as the lower panel of Fig. 5.