Ionization fraction computed using the W(CN)/W(N₂H⁺)ratio as a function of volume-weighted mean volume density, n. Contours correspond to the density of points of 1, 5, 25, 50, and 75 percent (from the most outer to the most inner contour). Colored dots are the binned trends of pixels from the different regions in Orion B (top panel of Fig. 1). The error bars show the weighted standard deviation of the points within each bin.