Distribution as a function of longitude of the full width at half maximum of the latitude distribution of various quantities described in the text, averaged in 1° longitude bins. The Hi-GAL 70-μm and 250-μm compact sources belonging to the band-merged source list are indicated with a full line blue and green histograms, where the FWHMs have been determined by a Gaussian fit to the source latitude distribution in each longitude bin. The black histogram represents the distribution of the MIPSGAL 24-μm sources, computed in the same way as for the Hi-GAL sources. The orange histogram represents the FWHM of the Hi-GAL 500-μm diffuse emission obtained simply as the amplitude of the latitude band encompassed by the 50% levels in Fig. 3. For each histogram, the thick lines of the same respective colour show the distributions after smoothing with a 5°-wide boxcar.