The weighted number overdensity map of PCL0217—“Bigfoot.” The upper left panel shows the distribution of the weighted number overdensity of galaxies with 3.73 < z_phot < 4.23 in PRIMER-UDS. The red open circles show the position of the eight confirmed subgroups observed by the JWST/PRIMER survey (J. S. Dunlop et al. 2021); the pink circle shows a previously reported overdensity of quiescent galaxies (QGs; M. Tanaka et al. 2024) covered by the JWST/BEACON survey (T. Morishita et al. 2025). The upper right panel shows the three-dimensional distribution of the 11 subgroups. An animated version of this figure is available at https://box.nju.edu.cn/f/d6e29ce33a704cd29439/?dl=1. The lower figures show the enlarged overdensity map of the eight confirmed subgroups covered by the PRIMER survey. The purple and red crosses show the location of massive (M_* > 10^9.5M_⊙) SFGs and QGs. The overdensities shown in the upper and lower panels are measured in circular areas with radius ﹩1^{\prime} ﹩ and 15″, respectively.