Density distribution of stars with ages of 5 < t < 50 Myr (top left), 50 < t < 100 Myr (top right), 100 < t < 200 Myr (bottom left), and 200 < t < 500 Myr (bottom right). The density distribution changes as a function of time, becoming gradually smoother. Over-arching structures corresponding to spiral arms are visible for all age intervals. The solid black lines indicate the location of the spiral arms from Reid et al. (2019).