(Top-right panel) Continuum-subtracted Hα image of NGC 4490. The 25th B-band magnitude elliptic contour is shown by a black solid line, along with the positions of SN 1982F (marked by a red star), SN 2008ax (marked by a red diamond) and the center of the galaxy (marked by a red circle). The slit position is shown, and a color code is used to present the N2 metallicity measurements at the position of each H ii region that we inspected. The slit width (1′′) has been enhanced to better show the colored patches. (Top-left panel) Flux at the Hα wavelength along the slit, shown as a function of the distance from the location of SN 1982F (marked by a dashed line). The N2 measurements are shown at the corresponding positions in the upper sub-panel. (Bottom panel) Metallicity gradient of NGC 4490. In the plot we include the measurements from Pilyugin & Thuan (2007), which match our N2 metallicity estimates. The linear fit on our measurements is shown by a solid line. The interpolated metallicity at the distance of SN 1982F is marked by a red square and its uncertainty corresponds to the fit error. The error bar (±0.2 dex) for our N2 measurements is shown aside. The positions of SN 1982F, SN 2008ax and nucleus are marked by vertical dotted lines. The solar metallicity (Asplund et al. 2009) and the LMC metallicity (Russell & Dopita 1990) are indicated by two horizontal dotted lines.