Data for New York census tracts, downloaded from https://www.census.gov/cgi-bin/geo/shapefiles/index.php?year=2023&layergroup=Census+Tracts and processed using https://mapshaper.org/.

Data resides in Gist: New York City Census Tracts.

See also:

• VizHub: Multivariate Choropleth Live Coded at Outlier
• Gist by Mourner: Quick example of generating GeoJSON contours from raster with d3 - reference example for creating GeoJSON from contours
• Gist: GeoJSON Contours Test