This example presents a hierarchical tree visualization of countries organized by continent and subregion, with the world at the root. The tree uses horizontal links and text labels whose font size decreases with depth, displaying all country names in a readable layout. The visualization supports pan and zoom via the d3.zoom interaction, applying the transform to a group element. The code builds the layout with d3.tree and d3.hierarchy, renders links using d3.linkHorizontal, and loads the hierarchical data from a JSON file.