Profiles of Loop I in total intensity at 408 MHz (Remazeilles et al. 2015) and in our combined Planck-WMAP polarized intensity image at 28.4 GHz. Profiles are along radial cuts beginning at the nominal centre of the loop, and are averaged over a 10°-wide sector in position angle, at position angles 75° (solid line), 50° (dotted), and 25° (dashed). They cross the North Polar spur at b = 22°, 43°, and 61°, respectively.