This example visualizes the hierarchical structure of world countries, grouped by continent and region, as a horizontal tree diagram. It uses a D3 tree layout with `d3.hierarchy` and `d3.linkHorizontal` to draw curved links, while node labels are rendered as SVG text elements with font sizes scaled by depth. The visualization supports pan and zoom interaction through `d3.zoom`, and data is loaded from a JSON file. Styling is applied via CSS, with teal link strokes and white text shadows for readability.