This choropleth map visualizes global income groups by coloring countries with a spectral color scale. It uses `d3.geoNaturalEarth1` projection and `d3.geoPath` to render the world map from TopoJSON data loaded via `world-atlas`. The map supports zooming through d3’s zoom behavior, and an accompanying legend built with `colorLegend` displays the ordinal scale values. Country data is joined from a TSV file, and hovering highlights each nation while a tooltip title shows its name and income group.