t-SNE projection of ∼420 000 RAVE spectra. The scaling in both direction is arbitrary, therefore the units on the axes are omitted. The colour scale corresponds to the gravity of the stars as computed by Kunder et al. (2017). Giants are shown in red and dwarfs in blue. Lighter shaded hexagons include fewer stars than darker ones. Over-plotted black dots indicate locations of RAVE stars in K2 Campaigns 1,3. Illustrated as stars are the RAVE-K2 objects studied in the present work, which fall in the metal-poor locus of the diagram.