A choropleth map colors countries according to their economy, using a categorical color scale and an interactive legend to filter by income group. Built with D3 v5, it projects geographic data from the world-atlas topojson using `geoNaturalEarth1` and renders each country as an SVG path via `geoPath`. The legend, generated through a separate module, allows clicking to highlight or dim countries by color value, while a zoom interaction adjusts the projection transform.