A hierarchical treemap visualizes the nested structure of world regions, from continents down to individual countries. The visualization uses a tidy tree layout to arrange nodes in a radial pattern, with each node represented as a circle and connected by curved links. The code employs `d3.hierarchy` and `d3.cluster` to compute the layout, rendering the result as SVG elements. Node labels show the region or country names, while the root node is highlighted with a different color. The example loads data from a `data.json` file containing the geographic hierarchy and uses `d3.select` to manage the SVG canvas.