Distribution of QSO systems at the linking length 70 h^-1 Mpc in x and y coordinates in two slices of z coordinate (upper panel: z ≤ 0 h^-1 Mpc, lower panel: z> 0 h^-1 Mpc). Grey dots denote quasars in systems with 10 ≤ N_QSO ≤ 24, blue circles denote quasars in systems with 25 ≤ N_QSO ≤ 49, and red filled circles denote quasars in systems with N_QSO ≥ 50. Black crosses denote quasar triplets at a linking length 20 h^-1 Mpc.