This interactive visualization displays yearly average temperature trends for individual countries from 1750 to 2013, using a multi-series line chart with a dropdown menu to switch between countries. The D3.js v7 code loads CSV data, aggregates monthly records into yearly averages, and renders an SVG line chart with axes, dots, and hover tooltips. It uses d3.csv, d3.rollups, d3.scaleLinear, d3.line with curveMonotoneX, and d3.schemeTableau10 to color the selected country’s line.