Integrated line intensity as a function of H₂ column density for the survey species detected in at least five column density bins. Top: traditional dense gas tracers (blue symbols). Bottom: additional tracers of dense gas (green symbols). For reference, each panel shows a linear relation that fits the average intensity of the highest column density bin (dashed line). For HCN(1–0), CN(1–0), N₂ H⁺(1–0), and C₂ H(1–0), the intensity includes the contribution from all detected hyperfine components. For CH₃ OH(2–1), the intensity includes the contribution from the A⁺ and E components. Depending on the transition, the lower limit of the intensity scale (0.05 K km s⁻¹) approximately corresponds to one to three times the noise level in the integrated intensity.