Two-dimensional distribution functions of polarization fraction p and column density N_H in the fields highlighted in Fig. 1. Top: Polaris Flare (magenta), Taurus (red), Chamaeleon-Musca (black), Microscopium (blue), and Pisces (green). Bottom: Ophiuchus (magenta), Pavo (red), Ara (black), Perseus (blue), and Orion (green). On both panels, the solid red lines show the upper and lower envelopes (see text) of the large-scale distribution of p and N_H, clipped below N_H = 2 × 10²⁰ cm^-2, while the dashed red lines correspond to p = 0 and the maximum value p = 0.198 (i.e., 19.8%) quoted in Planck Collaboration Int. XIX (2014).