Each circle is a term
(keyword from the publication)
that appears in at least 3 publications within the scope.
At most the 120 most frequent are shown.
The size is how many publications the term appears in (the «Occurrences» weight in the VOSviewer menu).
A line joins two terms that appear together in the same publication; the thicker it is, the more publications they coincide in.
The colour and the proximity group the terms that tend to appear together: each colour is a research line — the ones in the legend above. Two distant terms are almost never worked on together.
What is recent and what is not: in the VOSviewer menu (top right of the map) switch to the «Overlay» view and pick «Average year»: the terms are coloured by the mean year of the works they appear in, which shows which lines are alive and which have faded.
Network size:
116 nodes and 594 links, density 0.089
(0 = nobody is linked to anybody; 1 = everybody to everybody).