Galactic locations of a) OCs and b) ECs within the ATLASGAL range, superimposed over an artist’s conception of the Milky Way (Hurt’s from the Spitzer Science Center, in consultation with Benjamin), which was based on data obtained from the literature at radio, infrared, and visible wavelengths, and attempts to synthesize many of the key elements of the Galactic structure. The coordinate system is centered at the Sun position, indicated by the “⊙” symbol, and we have scaled the image such that R₀ = 8.23 kpc (Genzel et al. 2010). The two diagonal lines represent the ATLASGAL range in Galactic longitude (|ℓ| ≤ 60°). In panel a), we indicate the names of the spiral arms.