Left panel: moment zero quotient between the H¹³CN and HC¹⁵N ﹩J=0\to 1﹩ transitions. Right panel: moment zero quotient between the H¹³CN and HN¹³C ﹩J=0\to 1﹩ transitions. Blue contours are drawn at the 25%, 50%, and 75% of the peak H¹³CN moment zero emission. Cyan contours correspond to NH₂D emission as in Figure 15. In both panels, we indicate the N-red, NW- and Diffuse Ridge markers as in Figure 7.