2D histogram of velocity dispersion values against their Galactic longitude positions for all fit components with S∕N > 3. The dashed horizontal line indicates the velocity resolution of 0.21 km s⁻¹. In the horizontal and vertical direction we use 3415 and 200 bins, respectively. The blue line indicates the mean velocity dispersion value per Galactic longitude bin. The grey solid line is a smoothed version of the mean σ_v curve using a median filter with a kernel of ~3°. Dashed vertical lines show the approximate location of the giant HII region complex W43.