Maps of the HCO⁺/HCN ratio between the J = 1 → 0 (top left), J = 3 → 2 (top right) and J = 4 → 3 (bottom left) line integrated intensities in the region where the lines are brighter than 7% of their peak values. The J = 1 → 0 ratio varies between about 0.4 and 0.9. The isolated ratios shown at Δδ ~ 70′′ correspond to significant emission of ~30 K km s^-1 in both HCN and HCO⁺J = 1 → 0 lines. The J = 3 → 2 line ratio ranges from ~0.8 to ~1.7 while the J = 4 → 3 line ratio varies between ~1.0 and ~2.3. The contour lines correspond to the HCO⁺J = 1 → 0, J = 3 → 2, and J = 4 → 3 maps in the respective line ratios, and are defined as in Fig. 2. The HCO⁺J = 9 → 8 to HCN J = 8 → 7 line ratio is shown in the bottom right panel, for the region where the lines are brighter than 15% of their peak values. This ratio varies between about unity to ~4.8. The contour lines correspond to the HCN J = 8 → 7 maps and are the same as in Fig. 3. The area of the higher-J HCN and HCO⁺ ratio map is depicted with a dashed frame in the bottom left panel. The maps of the higher frequency lines were convolved to the larger beam of the lower frequency line before determining the respective ratios.