Distribution of QSO systems at the linking length 80 h^-1 Mpc in x and y coordinates in two slices of the z coordinate (upper panel: z ≤ 0 h^-1 Mpc, lower panel: z> 0 h^-1 Mpc). Grey dots denote quasars in systems with 50 ≤ N_QSO< 100; blue circles denote quasars in systems with 100 ≤ N_QSO ≤ 400, black triangles denote quasars in the second richest system with N_QSO = 421, and red filled circles denote quasars in the richest system with N_QSO = 920.