A choropleth map colors countries by their economic classification using an ordinal color scale derived from `d3.schemeSpectral`. A clickable color legend uses `d3.scaleOrdinal` to let the user select a specific economy type, which highlights matching countries via a CSS `.highlighted` class while dimming others. The visualization, built with `d3.geoPath` and `d3.geoNaturalEarth1`, renders an SVG world map with zoom support and tooltips, using COVID-19 case data merged from CSV files.