Contribution of the 139 new clusters to the surface density Σ_XY versus the projected distance d_XY. The distribution of all clusters is given in black (a), and the distributions of two age groups are indicated with green (log t = 8.3...9.0, b) and red (log t> 9.0, c). Solid curves correspond to the densities of known open clusters from the MWSC survey, the dotted curves include the new clusters, the dotted vertical line marks the completeness limit found for the total sample, and the dashed horizontal lines correspond to the average surface density for different age groups.