Chapitre 3 Perception : système visuel, marques et canaux, couleurs
3.1 TODO
3.2 Types de marques
3.3 Mappings in ggplot
figure from https://serialmentor.com/dataviz/aesthetic-mapping.html
3.4 scales in ggplot
figure from https://serialmentor.com/dataviz/aesthetic-mapping.html