A choropleth map colors world countries according to their income group, using a spectral color scale. The map is rendered as an SVG with a natural Earth projection, and hovering highlights a country in red. Built with d3.v5 and topojson, it loads geographic data from the World Atlas TopoJSON files alongside a TSV table of income classifications. The code uses `d3.geoPath`, `d3.geoNaturalEarth1`, `d3.zoom`, and a custom `colorLegend` component that maps ordinal color values to circles and labels.