HyperLeda isophotal diameter at 25.5 mag arcsec⁻² (from logd25 parameter) in arcminutes with respect to the B-band magnitude (btc parameter). Blue points represent the CS⁴G sample, and grey dots represent a larger sample from HyperLeda. The vertical and horizontal dashed lines represent the thresholds used to build the CS⁴G. There are some cases where some galaxies in the CS⁴G quadrant are not real galaxies meeting the criteria (as explained in Appendix B).