Cartoon illustrating the configuration of the UVCS O vi channel observations at the west limb: the UVCS field of view is shown in green as the projection onto the plane of the sky of the slit at the four positions. As an example of the data binning along the spatial direction, the slit at 1.5 R_⊙ is divided into the three-degree wide angular sectors within which UVCS data have been summed. The slit positions at the two PAs at the east limb are illustrated in the eastern panels of Fig. 2. As context images, we show an image from EIT-171, taken on January 2, 1998 when AR 8100 was at the west limb at a latitude of about −20deg, and a LASCO-C2 image, taken on the same day.