A choropleth map colors countries by income group using an ordinal color scale with a spectral scheme, drawing each nation with `d3.geoPath` and a Natural Earth projection. The visualization supports zooming via `d3.zoom` and includes a custom color legend rendered with SVG circles and text. Country names and income data come from TopoJSON and TSV files loaded from the world-atlas package. Hovering over a country reveals its name and income group in a tooltip.