Upper: comparison between the parallax-based distances of H II regions given by this work and the kinematic distances. The grey line is the equal line. Lower: distributions of the H II regions projected onto the Galactic disc, to better show the influence of updated distance parameters on the delineated spiral arm segments. The starting point and ending point of each arrow represent the positions of an H II region according to the kinematic distance and the parallax-based distance, respectively. The locations of H II regions based on the parallax distances are marked with blue dots. In the plot, the Sun is at (0, 8.15) kpc (Reid et al. 2019), while the Galactic Centre is at (0.0, 0.0) kpc. Q1–Q4 indicate the four Galactic quadrants.