This fork of a choropleth map colors world countries by income group using a spectral color scale. The visualization uses D3 v5 and the `geoNaturalEarth1` projection with `geoPath` to render country shapes from the world-atlas TopoJSON and TSV data. A custom `colorLegend` displays the ordinal color scale as circles and text, and zooming is enabled through D3’s `zoom` event. Hovering a country turns it red, and tooltips show its name and additional text.