A tree diagram visualizes the hierarchical structure of world countries, organized by continent and subregion, with the root labeled "Earth." The layout uses a horizontal tree, with nodes as text labels and red links connecting parent and child nodes. The visualization is built with D3.js v5, using `d3.tree`, `d3.hierarchy`, and `d3.linkHorizontal` to compute and draw the structure from a JSON file, while `d3.zoom` enables panning and zooming. Node text sizes decrease with depth, and the Playfair Display font is applied to labels.