A choropleth map displays countries color-coded by economy using D3's `geoNaturalEarth1` projection and `geoPath`. Users click countries to select them, which highlights the chosen nation while dimming others; clicking again deselects. A color legend using `scaleOrdinal` with `schemeSpectral` allows filtering by income group. Data loads from world-atlas TSV and TopoJSON files, with SVG rendering supporting zoom interactions via D3's `zoom` event.