A collapsible tree map displays the hierarchical structure of world countries, grouped by continent and subregion, using data from a JSON file. Each node is labeled with its geographic region name, with font size decreasing at deeper levels. The visualization is built with D3 v5, using `tree()` and `hierarchy()` layouts, rendered as an SVG with `linkHorizontal` paths. Pan and zoom functionality is implemented via `d3.zoom()`.