A radial tree visualization displays the hierarchical organization of countries, grouped by continent and subregion, with leaves arranged around a central "World" node. D3.js v7 computes the layout using `d3.cluster`, projecting nodes onto a circular coordinate system. The SVG rendering uses `d3.zoom` for panning and scaling, with links drawn as curved paths and text labels rotated and anchored based on depth and angular position. The data comes from a local JSON file containing country and regional classifications.