(a) The optical plane of the 4D Eigenvector 1 Parameter Space. The quadrants indicate the bins defined by Sulentic et al. (2002) and adopted here for composite spectra. Typical 2σ error bars are shown in the upper right corner. The horizontal dash–dot line indicates the nominal boundary between Populations A and B. The relative numerical contribution of from each population is 55 per cent in A and 45 per cent in B. (b) The number of sources considered in each bin along with a few (median) relevant measures in each bin are indicated. The square in the upper right is the legend of the numbers shown in each bin. Inside each bin (lower right square), we report the number of FR ii and core-dominated RL sources along with the estimated RL fraction. (c) Similar to (b), this time the numbers represent mean and standard deviations (in the parenthesis in each case).