Today we'll work with graph data once again. However, unlike in hierarchies where the emphasis is placed on the nodes and where they sit in a structure, we will instead be placing emphasis on the edges between nodes. For example, while it might be useful to compare GDP of regions using a treemap, you need a different visual metaphor if you want to show the trade *between* nations. Often, more structured visualizations work for this case, and today we'll try out a chord diagram. In the optional lecture we'll look at how to expand this approach to hiearchies and edge bundled arcs.