[CN]/[N₂H⁺], [CS]/[N₂H⁺] and [CN]/[CS] abundance ratios for the positions listed in Table 2 in the galacic plane (left) and the supershell associated with SN 41.9+58 (right) superposed to the N₂H⁺1 → 0 integrated intensity map (gray scale). For comparison, in the left column we plot the contours of the integrated intensity emission of the H (41) α line, and in the right, the integrated intensity emission of the SiO 2 → 1 line (García-Burillo et al. 2001). The white cross indicates the position of SN 41.9+58.