Emission map of the ℓ = 22° field that has been used to optimise the persistence and robustness thresholds used by DisPerSE. This map is overlaid with the skeletons obtained using a high robustness threshold that trace the high-column density regions shown in red (i.e. p = 1.4 and r = 2.5) and the inter-connecting skeletons obtained using a lower robust threshold that traces the lower column density connecting regions are shown in blue (i.e. p = 1.4 and r = 1.95).