Fig. 4

Inter-topic distance or principal coordinates plot of the hot topics, i.e., topics with a positive trend, showing the top 5 terms per topic; for better readability, only the top 60% of these topics are shown; main thematic gradients or differences may be identified by inspecting the topics along the principal coordinates from left to right and from top to bottom; terms are colored from light to dark grey according to their membership to clusters resulting from clustering the coordinates; the 4 cluster areas indicating main differing thematic fields are highlighted in grey; for avoiding text overlapping several topic terms are moved from their original positions, which are shown as dots, to which they are linked via a straight lines