This example demonstrates interactive filtering on a choropleth map of world economies, where clicking a color legend entry highlights matching countries and dims all others. Built with D3 v5, it renders GeoJSON features via `d3.geoMercator` and `d3.geoPath` in an SVG, with zoom support from `d3.zoom`. The legend uses `d3.scaleOrdinal` with `schemeSpectral`, and the map’s country opacity and stroke change in response to the selected value, sourced from the World Atlas TopoJSON dataset.