Distribution of the mock data (left panel), generated as described in Sect. 2.3. The x and z coordinates for each data point are drawn from four different Gaussian distributions with different means and covariances. The covariance is assumed to be diagonal. The y coordinates are generated to be correlated with the x coordinates with a correlation function consistent with Eq. (2)(see Table 1 for the correlation coefficients). The right panel shows the data space including the 3 × 3 square lattice neuron pattern after a successful training of the SOM. Neighboring neurons are interlinked in the picture. In addition, each sub-sample of data corresponding to one neuron, is drawn in the color of the specific neuron.