This example visualizes methane emissions across countries and years using a D3.js heatmap. Each cell’s color encodes emission values via `d3.scaleSequential` with the Viridis interpolator, while `d3.scaleBand` positions countries on the x-axis and years on the y-axis. The code loads CSV data from a GitHub gist, renders axes with `d3.axisBottom` and `d3.axisLeft`, and includes an interactive tooltip that displays exact CH4 values on mouseover. A horizontal color legend, built with the d3-legend library, accompanies the SVG chart.