Upper: map of the 353 GHz polarization fraction p at 1° resolution. The colour scale is linear and ranges from 0% to 20%. Lower: map of the 353 GHz polarization fraction uncertainty, σ_p, at 1° resolution in log ₁₀ scale. The colour scale is from σ_p = 0.1% to σ_p = 10%. The data are not shown in the grey areas where the dust emission is not dominant or where residuals were identified comparing individual surveys (see Sect. 2.4). The polarization fraction is obtained using the Bayesian method with a mean posterior estimator (see Sect. 2.3). The uncertainty map includes statistical and systematic contributions. The same mask as in Fig. 1 is applied.