This example shows the hierarchical structure of world countries, organized by continent and subregion, as a vertical tree diagram. The visualization uses a D3 tree layout to compute node positions and renders paths with `d3.linkVertical` for connecting links. Text labels display country names with font sizes scaled by depth. The SVG rendering supports zooming and panning through the `d3.zoom` API. Data is loaded from a local JSON file using `d3.json`, and the code relies on D3 v5's `select`, `tree`, `hierarchy`, and `event` modules.