Choropleth Map
This choropleth map colors countries by their income group using a categorical color scale based on d3.scaleOrdinal and d3.schemeSpectral. It renders geographic boundaries with d3.geoPath and a natural Earth projection, loading TopoJSON and TSV data from the world-atlas package. The visualization includes an interactive color legend built with reusable D3 code, supports zooming via d3.zoom, and highlights countries on hover with a red fill.