Relationship between the virial mass M_vir and the ¹²CO J = 1-0 luminosity $L_{{}^{12}\mathrm{C}\mathrm{O}(1-0)}$. The $L_{{}^{12}\mathrm{C}\mathrm{O}}$ luminosities are transformed to $L_{{}^{12}\mathrm{C}\mathrm{O}(1-0)}$ using $R_{\frac{3-2}{1-0}}\sim 2$ (Johansson et al. 1998). The filled red circles correspond to completely resolved clumps, whereas the empty red circles correspond to clumps where the minor axis is unresolved. The dashed line represents the relationship found for molecular clouds in the first Galactic quadrant by Solomon et al. (1987), $M_{vir}=39(L_{{}^{12}\mathrm{C}\mathrm{O}(1-0)}{)}^{0.81}$.