A choropleth map visualizes countries by their economic classification, with a color legend that doubles as an interactive filter. Users click legend items to highlight matching countries and dim others, while hovering over map regions reveals the country name and value in a tooltip. The map uses `d3.geoNaturalEarth1` and `d3.geoPath` for projection, `d3.zoom` for panning and zooming, and a `d3.scaleOrdinal` with `d3.schemeSpectral`. Data comes from the World Atlas TopoJSON and TSV files, with panning handled via SVG transforms.