Mollweide projections of the polarization fraction, p, and magnetic-helicity column, ℋ, produced placing the observer at the center of the filamentary structure described in Sect. 3.2 so as to emulate the structure of the Galactic arm in the solar neighborhood. For this specific model, both the direction of the local arm and that of the poloidal component of the magnetic field is , α_b = −20%, and p₀ = 26%. A Galactic coordinate grid centered at [l, b] = [0°, 0 ° ] and with steps of 30° is superposed.