Distribution of stars in cylindrical Galactic coordinates (R–z plane) colour-coded by their mean metallicities for all the stars in our sample (top), high-α selection (bottom left), and low-α selection (bottom right). We can see that dust near the Milky Way’s midplane significantly impacts our survey selection. We see a sharp negative metallicity gradient with respect to height above the disc plane in all stars and low-α stars. High- α stars have a shallower negative metallicity gradient.