This example shows a choropleth world map of population by country, with darker blue shades indicating higher values and a gradient legend on the right. It uses d3.geoNaturalEarth1 and d3.geoPath to project and render country boundaries from a TopoJSON world-atlas dataset. Population values are loaded via d3.csv from a GitHub gist and mapped to a d3.scaleSequential with the interpolateBlues interpolator. Labels display three-letter country abbreviations, while d3.axisRight and a linearGradient define the legend.