This example displays a choropleth map of the world, coloring countries by their sample population values using a sequential blue color scale. The map is rendered with SVG and D3.js’s `d3.geoMercator` projection and `d3.geoPath`. It loads real world geometry from a local GeoJSON file (`countries.geo.json`) and overlays tooltips via SVG `title` elements. Population data is provided as a static JavaScript object, with missing countries shown in gray.