A world choropleth map colors countries by economic classification using a categorical ordinal scale. Clicking a legend item filters the map, dimming unselected countries and highlighting the chosen category while clicking again resets the view. The visualization is built with D3 v5, using `geoNaturalEarth1` and `geoPath` for map projection and rendering, with pan and zoom enabled via `d3.zoom`. Data comes from the World Atlas TopoJSON, and the legend uses SVG circles with click handlers.