ROC curves for classifiers used in case A high galactic latitude a), case A low galactic latitude b) and case B c). In each case the left column shows the ROC curves (green for BDT, blue for MLP) obtained with the training sample using the ten-fold cross-validation method, as explained in Sect. 4.2. The right column shows the ROC curves obtained when applying classifiers to the test sample (solid line) or to the sample of labelled sources with flag (dashed lines).