D3 Country Bubble Chart
This bubble chart displays each country as a circle scaled by population, with hover tooltips showing the country name and population. Interactive radio buttons switch between grouping modes—combining all bubbles, clustering by continent, positioning at country centers, or sorting by population—and toggle circle fills between continent colors and country flag patterns. The visualization uses d3.forceSimulation with custom force configurations for each grouping, d3.scaleSqrt for radius scaling, and SVG patterns for flag fills. It loads data from a CSV file and animates transitions between the different layouts.