Two-dimensional histogram of Sample 1 in l − b plane and the results from SOM. (a): 2D histogram of the spatial distribution (l − b) of Sample 1, which only shows the bins with overdensities > 3σ. The NGC 2546 region, Pismis 5 region, and Alessi 43 region are each represented by a box in cyan, black, or magenta, respectively. The sources in the cyan, black, and magenta boxes are referred to as Sample 2, Sample 3, and Sample 4. (b), (c), and (d): 2D neural network produced by SOM, showing the neurons with a u value below the 99.85th percentile of the u distribution.