a) A Galactic longitude-velocity diagram made by taking the 3_0,3−2_0,2-weighted average of the R₁ PPV cube along Galactic latitude and using the n = 10⁴ cm^-3 curve from Fig. 6 to derive temperature. b) A Galactic longitude-velocity map of peak signal-to-noise along Galactic latitude, which is used as a mask in a). The apparently cold clumps at –80 km s^-1 in Sgr B2 and –90 km s^-1 in Sgr A are from a different line, HC₃N 24-23: the gas temperatures from these positions are meaningless. The apparent high temperatures around the cloud edges are artifacts caused by lower signal-to-noise ratios at the edges and should be ignored.