Location on the CCD of all stars with more than 100 good points in their light curve. The seventy brightest stars are plotted in blue, with the size of the marker proportional to the brightness of the star. Stars that lie closer than 50 pixels on the CCD from one of those bright stars are plotted in red. Crosses identify stars that have more than 20% bad points in their light curves (see Sect. 2.3).