Abundance properties of NGC 3521 traced by the fibres where the line flux errors ε < 0.3. Panela: Radial oxygen abundance distribution. The grey circles denote the R calibration-based abundances for the individual fibres. The red circles denote the median values of the oxygen abundances in bins of 0.5 kpc in radius, and the bars show the scatter in O/H around the median value of each bin. The line shows the O/H – R relation for those data. Panelb: Same as panel (a), but for the nitrogen abundances. Panelc: Intensity of the emission nitrogen line N₂ as a function of radius. The notations are as in panel (a).