Radial distributions of the emission line fluxes in NGC 628. Panels of columns 1–4: radial distributions of intensities of N₂ line (Col. 1), R₃ line (Col. 2), S₂ line (Col. 3), and R₂ line (Col. 4). Panels of rows a–d: IFU measurements from the surveys PINGS (row a), CALIFA (row b), PHANGS (row c), and VENGA (row d). The grey points denote the individual H II regions (panels of rows a, b, c) or individual spatial samplings (panels of row d), the red points with bars mark the median value in bins of 0.05 in R/R₂₅ and the scatter of each bin. The blue plus symbols are individual slit measurements. As only the red spectra were measured within the PHANGS programme then the R₂ line measurements are not available.