t-SNE similarity map of our sample GIRAFFE spectra. The three panels show the same map, each color-coded with a different physical parameter. While the relative distance of points in the map indicate the degree of similarity of the corresponding spectra, their X and Y coordinates themselves have no physical meaning. The map in this figure has been computed with perplexity 30. For our data, perplexity values between 20 and 50 produce qualitatively identical results.