CFHTLS MegaCam mosaic image in the i band with the X-ray contours superimposed in green; identified X-ray clusters are encircled in magenta circles, which have a radius r = r₅₀₀, and their XXL IDs indicated. The blue circles show the positions of the BCG in each cluster and the black crosses highlight the point sources excluded from the X-ray analysis. Contour levels are in logarithmic scale and they range from 4.5 counts/s/deg² to 30 counts/s/deg². North is up and east is on the left.