This choropleth map displays world countries colored by income group, with a legend showing the ordinal color scale. Built with D3 v5, it uses `d3.geoMercator` for projection, `d3.geoPath` to render geographic features from TopoJSON world-atlas data, and `d3.scaleOrdinal` with `schemeReds` for color encoding. Interactive zooming is enabled via `d3.zoom`. A custom color legend with animated circles transitions updates smoothly, and hover effects highlight individual countries.