Subregions of interest overlaid on the maps of each of the identified layer of the Orion B cloud, namely the low-velocity layer (top left), the intermediate-velocity layer (bottom left), and the main-velocity layer (right), from the ¹³CO (1–0) emission reconstructed by ROHSA. The green lines show the filamentary structures extracted from the C¹⁸O (1–0) emission. The red circles show the typical extensions of the Η II regions associated to massive stars (see Table 2).