A choropleth map uses color to encode values across world countries. D3’s `geoPath` and `geoNaturalEarth1` projection render the map from TopoJSON data, while a TSV file supplies per-country attributes. The map color-fills each country by its `scalerank` value using an ordinal color scale. A separate legend component displays the color-to-value mapping, and zooming is enabled via the `zoom` event.