Integrated intensity maps of dense gas tracers HCN, HNC, HCO+, and N₂H⁺ from SWAN at a common resolution of 3″ (top row from left to right), as well as from ¹²CO (PAWS, bottom left). We divide the disk into a center and ring environment (Colombo et al. 2014a), and the outer disk into northern and southern halves (bottom row, second panel from left). We add contours of integrated N₂H⁺ emission of 0.75, 2, and 4 K km/s to the environment map. We show the pixel-based integrated intensity distribution (in Kelvin kilometer per seconds) in various environments in the disk for all pixels in the FoV (colored shaded area), as well as for pixels where emission is detected (emission > 3σ, light gray shaded area) in the bottom right panels. The area of each histogram is normalized to unity. We indicate the median of all pixels (black dashed line) and median of masked pixels (dotted gray line) of each environment. The median represents the median value of logarithmic emission (med(log₁₀(I))). Pixels with negative emission are excluded in the logarithmic scaling of the histograms. Since CO is detected across most of the FoV and is used as a prior in the creation of the moment-0 map (Sect. 2.2), its masked histogram distribution agrees well with the unmasked one.