This visualization shows the hierarchical structure of world countries, organized by continent and subregion, using an expandable tree layout. The data is loaded from a local JSON file and rendered as SVG paths and text labels. The code uses d3.hierarchy and d3.tree to compute the layout, d3.linkHorizontal to draw the connecting links, and d3.zoom to enable panning and zooming. Node labels are positioned along the tree, with font sizes decreasing at deeper levels, and text shadows improve readability over the green link lines.