Radial metallicity profiles for the different sample galaxies. In each panel, the metallicity (estimated with the Pettini & Pagel 2004O3N2 method) is shown as a function of radius. On the main x-axis, the radius is normalised by r_eff, r, additionally we also give the x-axis in units of kpc, normalised by r_90, r, r_50, r and R_25, r for orientation. Filled circles mark all metallicity measurements that meet our quality criteria (see Sect. 3.3) and open circles that measurements that do not meet our criteria. The red dashed line shows the linear fit used to measure the metallicity gradient from the full metallicity profile and the orange dotted line the linear fit used to measure the metallicity gradient without the central 0.5 r_eff, r. The yellow shaded area, marks the radial regions between 0.5 and 2.0 r_eff, r, where e. g. publications based on CALIFA and MaNGA data products perform their metallicity gradient measurements. The text in the top right corner gives the GASS ID of the galaxy and the stellar mass.