discs [@fisher2017]. Modern methods of analysis of the largest coherent star formation scales such as two-point correlation function give results which are in good agreement with both classic methods (Gaussians, for instance) and theoretical Jeans lengths [@ali2017].

The turbulence predicts a relation $t\sim S^{0.5}$ between age $t$ and size $S$ of star formation regions [@elmegreen1996; @efremov1998]. A diffusion-driven expansion would produce a relation $t\sim S^2$ between age and size [@grasha2017]. @elmegreen1996 and @efremov1998 originally studied positions and ages of Cepheid variables and star clusters in the Large Magellanic Cloud and found that the average age difference between pairs of star clusters increases with their separation as $\Delta t {\rm (Myr)}\sim 3.3S {\rm (pc)}^{0.33}$ in the separation range from 8 to 780 pc. Later @marcos2009 found that the Milky Way star cluster pairs also satisfy the relation between age differences and their separation with the $0.40\pm0.08$ power if the effects of incompleteness and cluster dissolution are taken into account. @grasha2017 studied the connection between the age difference and separation of star cluster pairs in eight local galaxies and found that the age difference increases with the cluster pair separation to the $0.25-0.6$ power, with the maximum size, over which star formation 