A co-citation network consists of a set of nodes representing journal articles, and a set of edges/links representing the
co-occurrence of articles within the reference list of other journal articles (Leydesdorff, 2011). Therefore, two articles are
called to be co-cited if they appear together in the reference lists of other articles. That is, if both document A and B are
included in reference list of article C, then A and B are co-cited. Articles which are cited together more often are more likely
to present similar subject areas or be related (Hjørland, 2013). The initial co-citation mapping with Gephi revealed that there
are only 30 articles out of a total of 338 that have been co-cited by other articles within this sample.
In the following sections, we first use this co-citation concept to classify the existing literature of green ports and
maritime logistics, then we complete a similar analysis to classify the articles that are cited by these articles (referred to
as ‘seminal research areas’).