Fig. 6. Monitoring networks (black squares) obtained from the network of 74 monitoring stations by the drop–add algorithm . Tricube weight function, p = 1, anisotropic, and h_f = 120 (km), for the three design criteria (A–C) (see the Specification of Different Design Criteria section). Same for McLain weight function, h_f = 136 (km) (D–F).