[M/H] chemical inhomogeneities in the Galactic disc for samples A and C. Left panel: map of [M/H] excess for sample A, including the spiral arm contours from Poggio et al. (2021) and adopting a h_local = 200 pc and a longer scale length, h, that is six times higher. Right panel: same for sample C, including the spiral arm contours from Palicio et al. (2023) and adopting h_local = 200 pc and h_large = 1200 pc (i.e. six times higher).