Face-on 250 μm optical depth τ_dust obtained from MBBV fits plotted against normalized radius, R/R_opt; τ_dust has been corrected for inclination as described in the text. Points are coded by their oxygen abundance, with filled symbols corresponding to R/R_opt≤ 0.8 and open ones to larger radii. Only fits with ≤ 2 are shown. Both dashed and dotted lines show the mean 250 μm exponential scalelength (R_d/R_opt = 0.57 ± 0.5) derived as the average over all galaxies; the offset between the two lines corresponds to the mean difference between face-on orientation (dotted line) and the observed one (dashed line, with τ_dust not corrected for inclination).