Fig. 4.

Clusters considering articles cited 6 times at least. In the network visualisation, authors of the articles considered are represented by their label and by a circle. The size of the label and the circle of each item is determined by the weight of the item itself: the higher the weight of an item, the larger the label and the circle of the item. The distance between two items indicates the relatedness of the items in terms of co-citation links. For some items, the label is not displayed. This is done in order to avoid overlapping labels. The colour of an item is determined by the cluster to which the item belongs. The strongest co-citation links between articles are also represented by lines