Comparison of the observations to the Vallée (2008) model with four arms in the fourth quadrant of the Galaxy. We assumed a distance to the Galactic Centre of R₀ = 8.0 kpc. Cepheid distances (Majaess et al. 2009) are plotted as green points, open clusters and young groups from optical (UBVI) data (from several studies) are plotted as blue points, while red filled points show near-IR clusters studied using VVV data (Paper I, this study and Baume et al. 2010). Open red circles mark the Hii tracers (Hou et al. 2009) and the yellow dot marks the position of the Sun.