Graphics Reference
In-Depth Information
Chord Diagrams
Chord diagrams
are an effective method of visualizing reciprocal flow
between entities. In a chord diagram, entities are arranged in a circle, and
similar to a Sankey diagram, lines of flow linking entities are arranged side
by side at their origin and destination with thickness indicating the volume
of flow. What differs is that the lines are bidirectional, with varying widths
on either end indicating the volume flowing in either direction. Chord
diagrams are a good choice when flow is primarily bidirectional. You must
be able to see flow between but not
through
entities.
One common use case for chord diagrams is to visualize exchange of goods.
Figure 12-7
shows total trade between countries valued in U.S. dollars for
the year 2010. The chord width as it touches each country represents
outgoing flow of goods from country of origin, so the correct way to read
direction of flow is inward from the perimeter rather than outward, like two
arrows pointing at each other. The chord color is mapped to the country
with greater exports of the two, indicating the dominant direction of flow of
goods.
