This choropleth map colors countries by income group, with a legend showing the categorical color scale. The visualization uses D3 v5’s `geoNaturalEarth1` projection and `geoPath` to draw world boundaries from TopoJSON data loaded via `topojson.feature`. Country polygons are filled based on economy data from a TSV file, and hover effects highlight regions. Users can zoom and pan using D3’s `zoom` behavior, while the custom color legend is built with reusable D3 selection methods.