This is an im²Print and its one of the many tools of iRepertoire's data analysis platform, iRweb. Each rectangle in a given tree-map represents a unique CDR3 nucleotide sequence and the size of each rectangle denotes the relative frequency of an individual sequence. The colors for the individual CDR3 sequences in each tree-map plot are chosen randomly thus do not match between plots.
To draw the IgH CDR3 tree-map for each sequence sample, the entire rectangle was divided: 1st into a set of rectangles with each rectangle corresponding to a distinct VH gene segment; 2nd into a set of V-J rectangles with each rectangle corresponding to a distinct V-J; and 3rd into a set of V-J-CDR3 rectangles with each rectangle representing a distinct V-J-CDR3 combination. The rectangles are ordered based on area from largest at the bottom right to smallest at the top left. The size of an individual rectangle is proportional to the relative frequency for each V-J-CDR3 combination sequence. In order to distinguish neighboring rectangles, corners of each rectangle are rounded and each rectangles are colored randomly. Therefore, each rectangle drawn in the map represents an individual CDR3 nucleotide sequence.