Reachability Plot and clustering scheme for the alphabet M32K25. The bottom panel shows the Reachability Distance (neighbour distance) of all fragments in the order of the nearest-neighbour walk. Short distances correspond in general to high cluster density. The Reachability Distance scale is cropped to 0-14° to preserve details. The order of cluster extraction is illustrated in the top scheme, where each circle represents a cluster, its size inversely proportional to its Core Distance. The labels in the middle panel are those of the resulting Structural Alphabet; lines indicate the location of the cluster representative in the Reachability Plot. For each cluster (dent region in the plot) the corresponding representative was selected by lowest Core Distance (top scheme).