Extinction maps of Galactic molecular clouds (left) and corresponding Δ-variance (right). See Fig. 3 for further explanations. The red curves for NGC 2264 and Orion B represent ¹³CO 1 → 0 data from Bell Labs (see Table 1 and Bench et al. 2001). The green curve shows the spectrum for Orion A using ¹³CO 1 → 0 data from Bell Labs. The red curve for Rosette stems from ¹³CO 1 → 0 data from FCRAO (Heyer et al. 2006).