Meudon PDR code correlations among the L = 5 375 predicted lines from 27 chemical species, shown with the L × L matrix of absolute Pearson correlation coefficients. A value of exactly 1 for two lines means that there exists an exact affine relationship between their log-intensities. The black squares on the diagonal group lines from a common chemical species. For readability reasons, only the names of species with more than 100 lines predicted by the Meudon PDR code are displayed.