Sunburst Chart — also known as Ring Chart, Multi-level Pie Chart, and Radial Treemap — is typically used to visualize hierarchical data structures.
A Sunburst Chart consists of an inner circle surrounded by rings of deeper hierarchy levels. The angle of each segment is either proportional to a value or divided equally under its parent node.
All segments in Sunburst Charts may be colored according to which category or hierarchy level they belong to.
It is likely that the Sunburst Chart type of data visualization was developed to accommodate subunits of the Pie Chart’s primary segments (the earliest known example dates back to 1801, and it can be found in William Playfair's Statistical Breviary).