This prototype visualizes demographic distributions across New York City census tracts using geospatial contour lines. It blends overlaid choropleth-style contours colored by race (white, Black, Asian) onto a 3D orthographic projection, with an interactive pan-and-zoom interface. Data comes from the US Census Bureau’s 2023 Tracts shapefile and ACS estimates. The code uses `d3.geoOrthographic`, `d3.geoPath`, `d3.contours`, `@turf/turf` for point-in-polygon tests, and `RBush` for spatial indexing of tract boundaries.