This example shows a treemap visualization of population data, with three vertical columns of stacked rectangles representing different data groupings. The chart uses React to render SVG rectangles, with D3’s `scaleBand` and `scaleLinear` computing x and y positions and heights. Data comes from the United Nations World Population Prospects 2019. Mouse interactions highlight individual rectangles by adding a pink stroke via DOM event listeners. The visualization also includes a manually placed gray rectangle spanning multiple columns.