This example displays a world map with countries colored by population estimates using a linear color scale from red to dark red. The visualization uses `d3.geoMercator` projection and `d3.geoPath` to render geographic features from TopoJSON data provided by world-atlas. Population values and country names are loaded from a TSV file, while pan and zoom interactions are enabled through `d3.zoom`. Hovering over a country changes its fill to purple via CSS.