Radial gradient close to Galactic plane. Shown are data as traced by Cepheids (black dots from Genovali et al. 2014), open clusters (red circles from Genovali et al. 2014 and green circles from Netopil et al. 2016), and big magenta and black dots are the average metallicities for the GC region and |b| = 1, 2, 3 deg inner bulge fields discussed in this work. Errorbars refer to 1σ dispersions. The blue, dashed line indicates the relation noted by Hayden et al. (2014) for a large sample of APOGEE M giant stars covering a wide range of Galactocentric distances. The magenta dashed line indicates the relation found by Anders et al. (2017) for red giant stars with well-determined astero-seismological parameters.