A hierarchical tree layout displays the countries of the world organized by continent and subregion, with each country as a leaf node. The visualization uses `d3.tree` and `d3.hierarchy` to compute the layout from a nested JSON structure, rendering curved links with `d3.linkHorizontal`. Text labels position nodes with font sizes inversely scaled by depth inside an SVG, while `d3.zoom` enables panning and zooming the entire tree.