Low longitude CGPS Rotation Measures. Top panel: RMs of extragalactic sources (blue) and pulsars (orange). Second panel: RMs of extended emission using only interferometer data. The diagonal lines indicate the approximate location of the boundary across which the RM gradient occurs. Third panel: RMs of extended emission sources (red) and extragalactic sources (purple) as a function of Galactic longitude, averaged into 1° longitude bins. The error bars were determined as the standard deviations within the bins.