This bubble chart displays the correlation between population, urban population, and median age for several countries across different years, with bubble size encoding median age and color distinguishing the year. A tooltip appears on mouseover, showing country, year, population, and urban population. The visualization is built with D3 v7, using `d3.csv` for data loading, `d3.scaleLinear` for axes and bubble sizing, and `d3.scaleOrdinal` with `d3.schemeCategory10` for year colors, all rendered as SVG circles with interactive event handlers.