Degree of polarization vs. distance for all the stars with measured parallaxes by Gaia in the DP fields. Downward-pointing arrows represent the 3σ upper limit in polarization fraction when p∕σ_p < 3. Some distance error bars are too small to be seen. The dotted vertical lines correspond to the distance at which maximum E(B–V) is reached along the line-of-sight of each region according to Green et al. (2018). Empty circles denote the outliers defined in Sect. 4.2.