This example visualizes state population trends from 1910 to 2010 using colored lines for California, Michigan, and Texas. Hovering over the chart reveals a tooltip and a vertical line showing the exact population values for each state at that decade. The visualization is built with d3.scaleLinear, d3.line, and d3.axisBottom/axisLeft, and uses d3.json to load data from a JSON file. It renders as SVG, with a custom tooltip div positioned via d3.event coordinates.