This heatmap visualizes topographic elevation data from the `volcano.json` dataset, rendered directly onto a Canvas element. The code reads the JSON file using `d3.json` and maps values between 90 and 190 to a custom terrain-like color scale built with `d3.scaleSequential` and `d3.interpolateHsvLong`. Elevation values are converted to RGB colors via `d3.rgb` and written into `ImageData` with `putImageData`.