Number density per arcmin² of all objects identified by the arcfinder before applying geometrical and colour-selection criteria, which were applied in subsequent steps to identify the arc candidates. Since the more stringent constraints are not applied yet, these maps are dominated by spurious detections, which shows their distribution in the survey. The fluctuations in number density are expected because of the intrinsic inhomogeneous distribution of the sources and the large inhomogeneities of the image depth across the survey. We took this into account by measuring the noise locally. The three CARS fields, W1 (left), W3 (middle) and W4 (right), are shown.