Each cell is one codon at its fixed address CA = 4·pos1 + 16·pos2 + pos3. Shading shows how often the codon is used among its synonyms. The frame never changes; only the data layer does.
Panels follow the two-bit square of the middle base: A and G above, U and C below. Rows are position 1, columns position 3. Data: Kazusa codon usage database, via the python_codon_tables package. Met and Trp have no synonyms and always show 100%. Organisms are ordered by approximate genome size.