A choropleth map colors countries by their income group using a categorical ordinal color scale, with hover effects highlighting individual nations. Built with D3 v5, it renders geographic boundaries as SVG paths via `d3.geoPath` and `geoNaturalEarth1`, and loads world geometry from the world-atlas TopoJSON dataset. A custom color legend displays the categories, while zooming is enabled through `d3.zoom`. Data is processed asynchronously with Promises, merging TSV metadata with TopoJSON features.