Top: LOSs of C5 (in yellow), C45 (in green), and C50 (in red) drawn over the extinction density XY plane from J. L. Vergely et al. (2022) at 10 pc (d < 1.5 kpc) and 25 pc (d > 1.5 kpc) resolutions. The markers indicate the adjusted positions of optical polarization clouds. Y. Doi et al. (2024)’s results for the Sagittarius Arm are displayed in blue for comparison. Bottom panels: G-band extinction from Gaia Collaboration et al. (2023) as a function of the photogeometric distance for all Gaia stars within C5 (top), C45 (middle), and C50 (bottom). The solid blue line is the median A_G per distance bin. The vertical lines show the polarizing screens identified with BISP-1 using the optical (black) and NIR (orange) observations, corrected for the bias in the inverse parallax–distance relation (Section 5.1).