find that, also in space, stars from the Old sample are distributed homogeneously, whereas the young stars, and especially the CMG stars, exhibit stronger local concentrations. In Fig. \[YZ\_Vcut\_clumps\] we present the distribution of the 1844 stars of the CMG sample [[in the YZ plane]{}]{}. Although these stars were selected in a narrow velocity range, they show a relatively broad distribution in space with several remarkable local over-densities. This suggested to sub-divide CMG into four subgroups (CMG A0, CMG A, CMG B and CMG C). [[In Fig. \[YZ\_Vcut\_clumps\] we draw the borders of the four sub-groups with cyan, blue, green, and black lines respectively.]{}]{} The set of stars from CMG not contained in Groups A0 to C is called CMG Intergroup (CMG Z). Let us mention here that this subdivision is somehow arbitrary, and was guided by the appearance of these groups already in Fig. \[SCOCEN\].

The excellent quality [[($\langle\varpi/\sigma_\varpi\rangle \geq $10)]{}]{} of the individual parallaxes from [[*Gaia*]{}]{} DR2 in the region of CMG allows to invert them into individual distances. The four sub-groups are not only distinguished by their position on the sky, but also by their different distances from the Sun. Figure \[dist\_histo\] shows the distribution of the 