Survey area and the mask power spectrum. Top panel: CMB temperature anisotropies on the SPT-3G patch in galactic coordinates. The dark green line delimits the survey footprint. The vertical and horizontal bold black lines are the zero-longitude and zero-latitude coordinates, respectively. The SPT-3G patch covers roughly 4% of the sky. Bottom panel: mask power spectra as defined in Eq. (A.4) for SPT-3G and for the 143 GHz map used in the Planck cosmological analysis, which covers around 70% of the sky. The spectra have been renormalized by their first value for comparison purposes. Masks corresponding to small sky fractions, such as that of SPT-3G, have a shallower power spectrum than large ones. We emphasize that the mask used here does not include point-source masking.