Distribution of the SDSS data projected to the M_0.1r-z-plane. The top-left panel shows the volume limitation for different absolute magnitude thresholds (− 18.5, − 20.0). The bottom-left panel shows the distribution of the neurons after a successful application of the SOM to the SDSS data. The top-mid and bottom-mid panels show two different neuron-samples (N-Samples) corresponding to the depicted neurons from the trained SOM. In addition, the volume limitation used for the correlation comparison are depicted in both panels. The selected neurons hold sub-samples of data with a similar projected distribution compared to the volume-limited samples in order to compare the selection methods. The top- and bottom-right panels show reconstructed correlation functions for the volume limited sample with magnitude limits at − 18.5 (top) and − 20.1 (bottom) and for the corresponding neuron-samples. The range of each sub-sample in log (1 + δ) is indicated by the length of each reconstructed polynomial.