Sky distribution of all the PSZ1 clusters studied in this paper. The figure uses a Mollweide projection in Galactic coordinates. The Galactic plane is horizontal and centred at longitude zero. Red circles and blue triangles represent ITP (Sect. 2.1) and SDSS (Sect. 2.2) clusters, respectively, and the symbol size is proportional to the cluster mass. The shaded grey area represents the union mask used to produce the CMB map in the first Planck data release (downloaded from the Planck Legacy Archive). This mask excludes 27% of the sky, mostly in the region of the Galactic plane, the Magellanic Clouds, and point sources.