This visualization presents a world hierarchy as a tree, mapping the root node “World” to four continents—Asia, Europe, Africa, and North America—with two countries as leaf nodes under each continent. Node circles are color-coded by depth: blue for the root, purple for continents, and green for countries, with a legend clarifying the mapping. Using D3 v7, the code employs `d3.tree` and `d3.hierarchy` to compute the layout, then renders horizontal links via `d3.linkHorizontal` and draws circles and labels directly on the SVG, with text placement depending on whether a node has children.