Chord diagrams

A chord diagram is a graphical method of displaying matrix data, where nodes are distributed in a circular layout. Nodes are points radially positioned on the edge of a circumference, while links are lines that cross the circle to connect the points. It's also called a radial network diagram. It's a good choice for small datasets of undirected data with few connections, since directed links arriving and leaving a pair of nodes will overlap. The undirected matrix shown in the previous section, comparing border extensions of 13 countries, can be efficiently rendered as the following chord diagram:

A simple circular layout (non-ribbon chord diagram) showing South American countries (nodes) that have common borders.
The width of each line (link) is proportional to the extension of the border. Code: Examples/circle-1-borders-sa.html.

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