This choropleth map visualizes countries’ income groups using an ordinal color scale, coloring each nation from a world-atlas dataset. The map renders geographic boundaries via `d3.geoPath` with a natural Earth projection, and supports panning and zooming through d3.zoom. A legend, built with the custom `colorLegend` function, displays income group categories as colored circles. Hovering highlights countries in red, while tooltips reveal each country’s name and income group, sourced from the accompanying TSV metadata.