Distributions of the Galactocentric (top panel) and heliocentric (bottom panel) distances to the CHIMPS ¹³CO (3–2) sources, with spiral-arm assignments made by the Bayesian Distance Estimator of Reid et al. (2016), which uses the models of Reid et al. (2014). For clarity, thetop panel contains an inlay showing a close-up of the distribution in the Outer Galaxy. The bin sizes used for the Galactocentric and heliocentric distributions were 400 and 500 pc, respectively.