This example demonstrates density estimation of diamond prices and weights using contour lines. The visualization shows the distribution of carat and price data points, with concentric filled contour regions colored on a yellow-green-blue sequential scale to represent point density. The code uses d3.contourDensity for density estimation and d3.geoPath to render the resulting contour polygons as SVG paths. Data is loaded from a TSV file, with logarithmic scales applied to both axes for carat and price.