The 3D distribution of the selected MSCs from the N. V. Kharchenko et al. (2013) catalog in Sun-centered Cartesian coordinates (X, Y, Z in kpc). Marker color encodes the cluster age, and larger markers indicate higher estimated cluster mass M _cl (selection requires M _cl > 10³ M _⊙); the concentration near Z ≃ 0 traces the Galactic midplane.