A sample group of C3PO sources in the Taurus-Orion region, overlaid on the cold residual map in MJysr^-1. In this case, the elongation measure is ξ = 3.4. Black asterisks show the C3PO cold sources, solid lines indicate the MST edges and black dashed lines indicate the convex hull (defined in Sect. 3.3.2). The radius of the red dashed circle denotes R^c. Offset coordinates are used here, with the origin being the centre of the group.