The heatmaps below show, decade-by-decade, the rate of growth of Thematic Categories in comparison to the rate of growth of the complete Thesaurus in that decade. The vocabulary of the language as a whole increases over time (see here), and here this growth is treated as a baseline against which individual categories can be compared. Where a category's growth is less than would be expected in comparison with the general baseline, the appropriate heat map cell is coloured blue. Where a category's size is larger than would be expected, the heat map cell is coloured green. The shade of the cell is darker the further from the baseline the category's size is, with white indicating a close match between expected baseline size and observed category size. Rapid transitions between shades along the heatmap are indicative that categories are growing atypically.