Voronoi tessellations (VT) and X-ray images of the three superclusters (XLSSC-e: top, XLSSC-d: middle, XLSSC-f: bottom). Left panels: Voronoi tessellation using CFHTLS photometric redshift data. All galaxies within δz = ± 0.05 of the supercluster redshift are included. The side bar illustrates the colour-coding of the galaxy number-density. Only areas above the average number-density are coloured in the plots. Right panels: the corresponding X-ray maps overplotted with the positions of the studied areas (dashed circles) and of the X-ray detected clusters (large black circles with XLSSC ID numbers). The small black circles denote X-ray point-like sources above the luminosity limit (L_(0.5−2keV) > 2.7 × 10⁴² erg s^-1), while the red circles denote the ones with spectroscopic redshift consistent with the supercluster (within 2 × δz, see Sect. 4.1.2). The supercluster centres are marked with an X. The scale of the VT plots and their corresponding X-ray images is the same. The X-ray clusters can be easily identified in the high-density areas of the Voronoi plots. In the VT plots of XLSSC-d and XLSSC-f at least one more non-X-ray-detected overdensity can be seen, probably below the detection limit of the XXL Survey.