Aperture density map of a redshift slice at z ∼ 0.5 − 0.6. The colours show aperture density in the logarithm scale. The red contours indicate the edge of 3σ peaks, and the blue contours the edge of 1σ regions. The area outside the 1σ contours is identified as field. This kind of density map is plotted for all redshift slices to select cluster candidates and construct the field sample, which is used to make a statistical subtraction of the field average density. Stars indicate the confirmed cluster candidates analysed in this work.