A choropleth map shows the number of legal immigrants per country, with a threshold color scale ranging from gray to dark blue. Built with D3 v4, the visualization loads GeoJSON country boundaries and a CSV of immigration totals, then projects them using `d3.geoRobinson()` and draws paths with `d3.geoPath()`. Interactivity includes hover effects that highlight each country and display a tooltip with its name and total, plus a legend mapping color ranges to values.