Selection of individual frequency maps from Field 2 before (left) and after (right) the map-domain PCA filter. Because of the uneven sensitivity among the pixels, and to emphasize the relevant systematic effects, all maps have been divided by their white noise uncertainty. From top to bottom, each row shows maps that are dominated by (1) the turn-around effect; (2) the start-of-scan effect; (3) both effects simultaneously; and (4) neither effect. Both effects appear to manifest twice, on two slightly offset maps. This offset effect originates from the physical placement of the feeds, as they observe the fields as they are both rising and setting on the sky. In the equatorial coordinate system of these maps, the telescope scans vertically, and the field drifts from left to right.