Dense gas relations with N₂H⁺, with alternative dense gas tracers on the x axis, color-coded by the ELR function. Only points with a measurable ELR, which have a S/N greater than three for both lines, are included as colored points. Gray points are the remainder of pixels where the ELR is not measured, and the S/N of one or both emission lines is less than 3. The ELR accurately distinguishes “problem regions” where HCN and HNC no longer function as accurate dense gas tracers. HCO⁺ is a better dense gas tracer, in agreement with N₂H⁺ up to the most extreme ELR values. Yet even in this case, excluding ELR > 0.75 would ensure the most accurate dense gas estimates, assuming N₂H⁺ remains a viable dense gas tracer in the central regions. Pixels within the central 0.5 kpc have a dark border, for spatial reference.