A choropleth map colors countries by economic category using an ordinal color scale derived from d3.scaleOrdinal and d3.schemeSpectral. Clicking a legend item filters the map, reducing the opacity of non-matching countries and highlighting the selected category. The map uses d3.geoNaturalEarth1 and d3.geoPath to render world features from TopoJSON data, while d3.zoom enables panning and zooming on the SVG. Hovering a country turns it red via CSS.