Correlation between the λ and c residuals at a fixed halo virial mass, for the z = 0 halo population in the Bolshoi-Planck simulation, represented with the black solid contours (containing 68%−95% of the halo population). The red dashed contours are the 1- and 2-σ contours of the 2D normal distribution defined with the covariance matrix calculated from the distribution of points in this plane.