Distribution of young DR3 Cepheids in $\mathrm{log }R/R_{\odot }$ and ϕ′, as in Fig. 3, but the positions of the arms are overplotted as derived using the Cepheids with azimuths $-{120}^{\circ }<{\varphi }^{\prime }<0^{\circ }$. Red corresponds to the Scutum arm, blue to the Sgr-Car arm, orange the local Orion arm, and green the outermost (Perseus) arm. The solid (dashed) lines show the arms using the pitch angles found from the maximum strength (prominence).