Fraction of OCs for different age bins across the Perseus (left), Local (middle), and Sagittarius (right) Arms. The x-axis represents the Galactic azimuth (θ_G) explored for a circular section centred at the Galactic centre, at a distance of 10 (left), 8.3 (middle), and 7 (right) kpc. The y-axis gives the number of OCs in each θ_G bin over the total number of OCs in the whole circular section. Solid blue lines, dotted orange lines, and dash-dotted green lines correspond to clusters in 0−30 Myr, 30−80 Myr, and 80−120 Myr age bins. The numbers of OCs in each panel for the 0−30 Myr, 30−80 Myr, and 80−120 Myr age bins are as follows: 40, 35, and 13 for the Perseus Arm; 46, 56, and 24 for the Local Arm; and 21, 15, and 9 for the Sagittarius Arm, respectively.