This example visualizes demographic patterns across New York City census tracts as smooth, colored contour layers, with orange representing the Black population and green representing the White population. The contours are computed from a grid of sampled values using spatial indexing with RBush and point-in-polygon tests via Turf. City labels appear for municipalities above a population threshold, and the orthographic projection supports pan and zoom interactions. The visualization relies on D3’s `geoPath`, `contours`, `geoTransform`, and `scaleSequential` APIs, with data sourced from the 2023 Census Tracts and ACS demographics.