Distribution of the H ii regions analysed in this study projected onto the Galactic plane. The numbers close to the circles show distances to the Galactic centre in kpc. Red circles denote regions with abundances estimated with direct methods, black squares represent results from tailor-made models, and blue squares plot the abundances obtained from the relation. Regions with chemical abundances estimated with two methods are represented twice. The Sun and M 42 are also represented at R_G = 8.5 kpc (black solar symbol) and R_G = 8.95 kpc (black cross), respectively.