Uncovering the Hidden Routes: Algorithms for Identifying Paths and Missing Links in Trade Networks

A network is a simple yet powerful tool for representing a set of relations in the real world. For instance, to represent direct business relations between several people, we can sketch a network where each person is represented by a node and any two people that have done business together are connected by a link. A naive analysis of this network gives a picture of the direct connections between individuals, that is, who has done business, in person, with whom. However, for several network applications it is important to observe more complicated structures, other than the direct connections between the nodes. An example comes from applications in trade networks, where goods are exchanged between several people. In this case, it is important to keep track of the paths that specific goods have traversed in a network; in other words, we want to know the exact sequence of nodes through which a specific item was exchanged. Unfortunately, in some studies of trade networks we may not always know the exact path that certain items followed in the network. This is frequently the case with networks that represent trade relations between sites in an earlier historical period; knowledge of the exact trade paths in such networks has not survived and only fragmentary data is available (Sindbæk 2007, 2013; see in this volume Peeples et al. 2016). The same problem also arises in modern trade networks, when the transactions involved are the result of illegal activities. Such an example is the modern trade network in illicit antiquities. During recent decades, thousands of antiquities were illegally excavated worldwide and exchanged via a global trade network. During the late 1990s and 2000s, the combined efforts of forensic archaeologists and police investigators uncovered a considerable part of the trade network that handled illicit Italian and Greek antiquities in particular (Gill and Chippindale 2006; Gill and Tsirogiannis 2011; Godart et al. 2008). However, a large part of the activities that took place within this network remain unknown and there are some transactions that police investigations were not able to trace.