Nested Pie Chart

Introduction: A pie chart divides a circle or ellipse into slices, where the size and color of each slice is based on some attributes of the elements it represents. For example, one can show the constituents of a stock porfolio in a pie-chart, where each slice will be occupied by one stock and the size of the slice will be decided by the total value of the portfolio, and the color determined by percentage price change.

A Nested Pie Chart extends the functionality of a pie-chart by adding letting it represent a tree data model, thus making it a elliptical heatmap. The algorithm is as follows:

1. Draw a pie-chart that represents the first level of child nodes of the root-node
2. Sub-divide each sector of the pie-chart in 1. into smaller slices by drawing arcs with radius determined by a child node of the nodes represented in 1.
3. The geometrical shape obtained in 2. is further sub-divided by radial slices, the resulting shape looking like a slice of a cake.

The alogrithm above is illustrated by a couple of screenshots below:

Root Level Screenshot

Child Level Screenshot