Further Matrix Operations

Beyond breaking unknown nodes and collapsing the trees of subdivisions, we can do a number of other operations on the raw matrix in Figure 14-5. As with any adjacency matrix, we can sort (or permutate) the columns and lines along the horizontal and vertical axes, without losing any information (Bertin 1981; Bertin 2001). We can also transpose cells such as Monument-Event to Event-Monument, or even the whole Bibliography column to a Bibliography line, effectively reversing the direction of the links. Finally, we can merge equivalent node types—such as Provenance and Preservation Events, Monuments and Replicas, or Bibliography and Citation—by creating node supertypes, such as Event, Monument, and Bibliography. The merge reduces the number of columns and lines in the matrix and allows each cell to occupy more spa....