Pairwise relationships between the three network metrics (a-c).

The purple-point groups deviating from the main cluster are identical in (b) and (c), representing stations (purple dots) that are isolated from the main body (gray dots) of the network (d). Univariate linear regression with the ordinary least square method shows that all pairwise relationships are significant at the level of P<0.001. The purple dots as deviants are excluded from the regression analysis in (b) and (c). All metrics are log-transformed and then normalized to 0–1.