Figure 2.

Detailed flow diagrams of the algorithms used to generate a polar map. (a) Traffic computes the betweenness centrality of each node (Freeman 1977; Newman & Girvan 2004) and divides disconnected groups of nodes in islands; (b) modularity generates the modules via the Q-modularity algorithm (Clauset et al. 2004) (c) The ring ordering procedure (Valente & Cusick 2006) finds a good ordering for the modules; and, finally, (d) the polar map algorithm calculates the polar coordinates of each node based on the results from (a–c).