Radial distribution of the current Cepheid sample (colored circles) projected onto the Galactic plane. The symbols are color-coded (see the color bar on the right side) according to the distance from the Galactic plane. The dotted annuli display muliples of 5 kpc of the distances from the Galactic center. The position adopted for the Sun is at X = 0 and Y = 8.127 kpc (GRAVITY Collaboration 2018). The colored diamonds show the locations of highmass star-forming regions used by Reid et al. (2019) to fit the spiral arms. They are color-coded according to the spiral arm association. The long bar of the inner part of the Galaxy is indicated with a shaded ellipse (Wegg et al. 2015). The solid curved lines trace the Milky Way spiral arms from Reid et al. (2019) and from Sun et al. (2015, Outer, Scutum, and Centaurus arms).