This choropleth map visualizes world population by country using a blue sequential color scale. It loads GeoJSON country boundaries and a CSV of population data, joining them by ISO3 country codes. The map is rendered with D3.js, using `d3.geoNaturalEarth1` projection and `d3.geoPath` to draw SVG paths. Countries with missing data are shown in gray. Hovering over a country reveals a tooltip with the country name and formatted population. A gradient legend displays low-to-high population values with tick marks.