Fractal dimension for the spatial distribution of open clusters vs. distance. (a) In the solar neighborhood and (b) in the Galaxy. Note that the fractal dimension here is calculated based on the spatial distribution of individual clusters, rather than the internal distribution of member stars within each cluster, as discussed earlier. A cluster is represented as a single point in the 3D space, which is the median position of all stellar members. (a) Pink circles and orange triangles represent the fractal dimensions for the distribution of the Pang catalog clusters and Hunt catalog clusters, respectively. The blue bar indicates the extent of the Local Bubble. (b) Blue circles show the fractal dimension for the distribution of 3457 Hunt catalog open clusters across the Galaxy. The approximate locations and ranges of the Galactic arms are indicated in pink (Local Arm), brown (Perseus Arm), purple (Scutum-Centaurus Arm), red (Norma Arm), and orange (Outer Arm).