This is the Chord diagram section of the gallery. If you want to know more about this kind of chart, visit data-to-viz.com. If you're looking for a simple way to implement it in d3.js, pick an example below.
A few notes on chord
Chord diagram is probably one of the most difficult graph to build with d3. Here are a few reminders:
Everything relies on the d3.chord() function. This function takes as input a square matrix of flow. The output is an array of chords.
Each chord as a source and a target. For each group it gives info like the angle of start and end, the flow value, the node index,
It's important to understand that a chord diagram is composed by 2 elements: the links, and the nodes. Nodes are like a donut plot
The nodes are drawn using the arc() function. The links with the ribbon function().