Ratio of the α_CO(1–0) calculated from the gas-phase metallicity inferred only from nebular emission lines (${\alpha }_{\mathrm{C}\mathrm{O}(1-0)}^{\text{em.lin.}}$) to the combined map (${\alpha }_{\mathrm{C}\mathrm{O}(1-0)}^{\text{comb. }}$) vs the ratio of the number of pixels within the emission lines-map to the number of pixels within the combined map. The colour bar shows the number of resolution elements (θ_PSF) that constitute the gas-phase metallicity map from the nebular emission lines. The red horizontal lines (from bottom to top) indicate the 25th, 50th, and 75th percentiles of the α_CO(1–0) ratio distributions. Additionally, α_CO(1–0) values from the left panel come from global measurements, while on the right panels beam measurements are displayed.