Radial distribution of N/O plotted versus Galactocentric radius. Black points represent N/O abundances obtained with the direct method. The two lines represent the fit to data in two distances ranges: within 12 kpc from the Galactic centre (blue dot-dashed line) and farther than this limit (red dashed line), see text for details. The Orion nebula, the Sun and Magellanic Clouds are represented as in Fig. 13.