All-sky map, in Aitoff projection, of the observational Galactic Faraday depth, FD_obs, as reconstructed by Oppermann et al. (2015). The map is in Galactic coordinates (ℓ,b), centered on the Galactic center (ℓ = 0°,b = 0°), and with longitude ℓ increasing to the left and latitude b increasing upward. Red [blue] regions have positive [negative] FD_obs, corresponding to a magnetic field pointing on average toward [away from] the observer. The color intensity scales linearly with the absolute value of FD_obs up to | FD_obs | = 400 rad m^-2 and saturates beyond this value.