Sample nebular extinction. Top: E(B − V) as a function of galactocentric distance D for individual H II (black dots) and DIG regions (blue diamonds). Uncertainty-weighted averages in bins of 20 objects are also shown in red circles for H II and in orange diamonds for DIG. The propagated error bars are often smaller than the markers. The x-axis position of each uncertainty-weighted average is the average galactocentric distance for the dendrograms inside each bin. Bottom: 2D map of E(B − V).