This radial tree visualizes the hierarchical structure of world countries, organized by continent and subregion, using data from `data.json`. Built with D3 v4, it renders an SVG and supports panning and zooming via the `d3.zoom` interaction. The tree layout is computed using `d3.hierarchy` and `d3.cluster`, with links drawn as curved paths. Text labels use font sizes scaled by depth, and the layout is adapted from Curran Kelleher’s World Countries Hierarchy block.