Planck 353 GHz polarization maps at 1° resolution. Upper: Q Stokes parameter map. Lower: U Stokes parameter map. The maps are shown with the same colour scale. High values are saturated to enhance mid-latitude structures. The values shown have been bias corrected as described in Sect. 2.3. These maps, as well as those in following figures, are shown in Galactic coordinates with the Galactic centre in the middle and longitude increasing to the left. The data are masked as described in Sect. 2.4.