Distribution of star clusters in the XY-plane centred at the position of the Sun. Blue squares mark the youngest (log t ≤ 7.9) clusters, black plusses show clusters with 7.9 < log t ≤ 8.3, black crosses correspond to clusters with 8.3 < log t ≤ 8.75, while red circles represent old clusters with log t > 8.75. The dashed magenta thick curve is the Perseus spiral arm fitted by a two-arm model of the spiral pattern with a pitch-angle of  − 6°. The large black dashed circle around the Sun indicates the completeness area of the COCD sample. The black solid circle marks the estimated probable completeness area of MWSC.