This choropleth map colors countries according to their income group, using a spectral color scale with a clickable legend that displays the categorical values. The map is rendered with SVG paths generated by `d3.geoPath` and a `geoNaturalEarth1` projection, with zooming enabled via `d3.zoom`. Geographic data comes from the World Atlas TopoJSON, joined with country names from a TSV file. The color legend is built with `scaleOrdinal` and custom `colorLegend` functions.