This scatter plot displays the relationship between population density and median age for various countries. Circles are colored steelblue and turn orange on hover, with a tooltip revealing the country name and both values. Built with D3.js, the visualization loads data from `mergedata.json` and uses `d3.scaleLinear` for axes, `d3.axisBottom` and `d3.axisLeft` for ticks, and SVG circle elements with mouse event handlers to control tooltip opacity.