Top row: comparison of magnitude distributions for the KiDS-DR3 photometric FIDUCIAL sample (black) and the spectroscopic redshift calibration dataset (red). Bottom row: similar comparison but for selected magnitude-colour planes. The contours are linearly spaced. The FIDUCIAL sources are used as the reference for weighting the spec-z training set in the derivation of photo-zs for the full catalogue (Sect. 4.4). See also Fig. 3 for colour-colour plots where weighting of the training is additionally illustrated.