Top panel – IRS/SL map of the apparent silicate strength S_sil estimated at 9.85 μm. Bottom panel – Silicate-based extinction A_V(9.85 μm) map estimated from the average visual extinction to silicate optical depth ratio A_V/τ(9.7 μm) = 18 for the local ISM (Roche & Aitken 1984; Rieke & Lebofsky 1985) and assuming τ(9.7 μm) ≈ S_sil(9.85 μm). The contour lines of the stellar light-based extinction A_V(H − K) of Fig. 7 are overlaid on the A_V(9.85 μm) map (color pixels).