This visualization shows the hierarchical structure of world countries, organized by continent and subregion, as a tree diagram with horizontal links and labeled nodes. The layout uses the `d3.tree` and `d3.hierarchy` functions to compute node positions, while `d3.linkHorizontal` draws the connecting paths. Node labels are rendered as SVG text with font sizes scaled by depth, and the entire tree supports pan and zoom through `d3.zoom`. The data is loaded from a local JSON file via `d3.json`.