Circles on a map
This example visualizes world population data by mapping 2018 population estimates as scaled circles positioned at country centroids. Using a natural Earth projection, countries are rendered as SVG paths with color coding—gray for data availability and pink for missing data. The visualization supports hover effects, zooming via the `zoom` event, and includes a size legend built with a custom `sizeLegend` component. Data processing combines CSV population statistics with TopoJSON geometries using `topojson.feature`, while circle radii are scaled through `d3.scaleSqrt`.