This visualization displays the hierarchical structure of world countries, organized by continent and subregion, as a horizontal tree diagram. The root node represents the data source, with branches expanding outward to reveal geographic groupings and individual countries. The code uses D3.js v5, implementing a tree layout with `d3.tree()` and `d3.hierarchy()` to process hierarchical JSON data. Nodes are rendered as SVG text elements connected by horizontal links generated with `d3.linkHorizontal()`, and the entire visualization supports pan and zoom through D3’s zoom behavior.