Impact of the observed chemical inhomogeneities on the Galactic gradients. Upper panel: map of the mean metallicity in the Galactic plane for Sample A, with overlaid azimuthal slices of 5°, from ϕ = −20° to ϕ = 20°. Lower panel: median metallicity as a function of Galactocentric radius R for different slices in Galactic azimut ϕ for Sample A (filled dots) and Sample C (open dots). Regions that might be associated with the Perseus (red, letters ‘a’–‘e’), Local (green, ‘f’–‘n’), and Sagittarius/Scutum (blue, ‘o’–‘x’) arms are shown as coloured regions in both the upper and lower panels.