Galactic longitude-velocity distribution of all filaments. The background image shows the distribution of molecular gas as traced by the integrated ¹²CO (1-0) emission (Dame et al. 2001); the colour bar on the right shows the relative intensity of the emission. The magenta circles mark the positions of the ATLASGAL filaments while the cyan squares show the positions of other filamentary structures reported in the literatures (see Sect. 5.1 for details). The coloured lines trace the location of the spiral arms taken from the model by Taylor & Cordes (1993) and updated by Cordes (2004). The blue, green, yellow and orange curves trace the Norma, Scutum-Centaurus, Sagittarius and Perseus arms, which are the four main spiral arms, while the red curve tracers the Near 3-kpc expanding arm (Bronfman et al. 2000).