Top: change of differential extinction per distance with distance for SNR G22.7-0.2 (red line) and the surrounding area (grey lines). For the SNR sightline, there are two significant gradients marked as red dashed lines: the larger one at 4.74 kpc with mag kpc⁻¹, and the smaller one at 3.11 kpc with mag kpc⁻¹. The blue dotted lines indicate the locations of half maximum half width of the profile, which represent the distance errors. For the surrounding area, the extinction gradients are weaker and marked as the grey dashed lines. Bottom: distribution of differential extinction per distance for the sightline of molecular cloud G15.15-0.7.