Comparison of the oxygen abundance at the optical radius in the Milky Way and in the structural Milky Way analogues. Panela1: Oxygen abundance at the optical radius of the galaxy as a function of its stellar mass. The grey circles designate the structural Milky Way analogues, the square marks the Milky Way, and the cross is the NGC 3521. Panel a2: Same as panel (a1), but the grey circles show a total sample of galaxies from Pilyugin et al. (2023) (not only the structural Milky Way analogues). Panel b1: Oxygen abundance at the optical radius of the galaxy as a function of the optical radius. The designations are the same as in panel (a1). Panel b2: Same as panel (b1), but the grey circles show a total sample of galaxies.