This choropleth map colors world countries by their economy group, using a spectral color scale. Users can click any color legend swatch to isolate that economy category, while all other countries fade to low opacity. Hovering a country highlights it in red. The map renders with `d3.geoPath`, updated via a D3 zoom interaction, while `d3.scaleOrdinal` and `d3.schemeSpectral` drive the categorical colors. Data comes from the `world-atlas` package, joined with TSV income-group values.