This heatmap visualizes Earth’s surface temperature variations from 1753 to 2015, with each cell representing a month’s temperature relative to a base value. The color scale uses a custom ordinal scheme ranging from dark red (warm) to dark blue (cool), while hovering over a cell displays a tooltip with the exact month, temperature, and variance. The visualization is built with D3 v5, using `d3.scaleTime` for axes, `d3.scaleOrdinal` for colors, and `d3-tip` for interactive tooltips. Data comes from a JSON file containing `baseTemperature` and `monthlyVariance` values.