Classical Cepheids (black dots) in the Galactic plane. The Galactocentric distances are derived from mid-infrared photometry to minimize the effect of reddening. The spiral arms delineated by Reid et al. (2019) are over-plotted using the same color-coding as in the original paper. Two segments are plotted in red as they presumably belong to the same Norma-Outer ring. Concentric circles are shown every 4 kpc to guide the eye. The Galactic center (black filled circle) is at (0,0) and the Sun (yellow star) at (8.275,0).