A choropleth map colors countries by economic classification using an ordinal color scale, with a linked legend for interactive filtering. Clicking a legend category dims non-matching countries and highlights selected ones, while clicking again clears the filter. The visualization uses d3.geoPath and d3.geoNaturalEarth1 for map projection, and d3.zoom for pan and zoom. Data comes from world-atlas TopoJSON and TSV files; colors are applied via d3.scaleOrdinal with the GnBu scheme.