Ratio of the measured over the idealized noise for Voronoi zones comprising N_z spaxels. The idealized noise is that derived under the assumption of uncorrelated errors, while the measured one is obtained from the detrended standard deviation of fluxes in a ± 45 Å range around 5635 Å. Gray dots represent β_z values for 99267 spaxels from 109 galaxies. Circles show the median β_z for each N_z, and the solid line shows Eq. (4). The top panel shows the histogram of N_z values (notice the logarithmic scale).