The U-Matrix was colored as a geographical map with brown or snow-covered heights and green valleys. Thus, valleys indicate clusters and watersheds indicate borderlines between different clusters. The dots indicate the so-called “best matching units” (BMUs) of the self-organizing map (SOM), which are those neurons whose weight vector is most similar to the input. A single neuron can be the BMU for more than one data pint or subject, hence, the number of BMUs may not be equal to the number of subjects as in the present case. The BMUs were differently colored to analyze the distribution of subjects across the cluster structure of the data space. Left: Localization of cluster memberships on the U-matrix, for comparison with the further presentations, using a coloring for the BMUs corresponding to the membership to the machine-learned clusters of olfactory subtest results patterns. Middle: Distribution of etiologies associated with the subjects’ olfactory function across the U-matrix respectively cluster structure. Right: Distribution of the olfactory diagnoses (anosmia, hyposmia, normosmia) across the U-matrix respectively cluster structure. The figures displaying geographical map analogies have been created using our R library “Umatrix” (M. Thrun, F. Lerch, Marburg, Germany, http://www.uni-marburg.de/fb12/datenbionik/software ; file http://www.uni-marburg.de/fb12/datenbionik/umatrix.tar.gz).