This visualization displays the hierarchical structure of world countries, organized by continent and subregion, as a horizontal tree diagram rendered with SVG. The layout is generated using `d3.tree` and `d3.hierarchy`, with links drawn via `d3.linkHorizontal`. The data, sourced from `data.json`, is loaded using `d3.json`, and the tree layout is sized to fill the browser window based on `document.body.clientWidth` and `clientHeight`.