This example visualizes World Bank GDP per capita data for 2020 as a choropleth map, using a natural Earth projection and a quantile color scale with the YlGnBu scheme. Missing data appears gray. The map renders country boundaries from TopoJSON fetched via `topojson.feature`, while CSV data is parsed with `csvParse` and joined to country codes using a `Map`. The visualization uses `d3.geoPath`, `geoNaturalEarth1`, and `d3.scaleQuantile` to encode values as fill colors.