Maps (in equatorial coordinates) of the parallax errors in the three selected iterations k = 5, 20, 135 (top to bottom). The left column shows the median of the parallax error ϖ^(k) − ϖ^true, while the right column shows the median of the absolute error |ϖ^(k) − ϖ^true|; each map cell (of about 0.84 deg²) shows the colour-coded value computed for the sources located in that cell. Empty cells are shown in black. On every map plot the top left label indicates the iteration number and the top right label is the maximum value of the displayed range in μas. See text for further details.