Density map of three orientations of the GP of YSOs associated with SFRs with ages of t ≲ 10 Myr. In the upper left panel, the Sun is at (0, 0), the x-axis is directed towards the Galactic centre, and the y-axis is towards the direction of the Galactic rotation. Dashed white circles are drawn at distance steps of 500 pc. In the upper right and lower left panels, the z-axis is perpendicular to the GP. Colour bars indicate the surface densities, that is, the number of stars per bin and per pc². Some known SFRs are indicated. The numbers from 1 to 9 in the upper right and bottom panels indicate the position of the clusters indicated in Fig. 5 (upper left panel).