GeoJSON Map Viewer

Simon Willison released a new GeoJSON Map Viewer tool that displays GeoJSON files on a map and exports them as PNG images, built with assistance from GPT-5.6-Sol, Claude Code for web, and Fable 5.1. The tool was created to help Natalie gather maps of local political boundaries, and Willison used ChatGPT Work to generate GeoJSON polygons for the Granada Community Services District and the Midcoast Community Council.

Tool: GeoJSON Map Viewer https://tools.simonwillison.net/geojson I was helping Natalie gather some maps of local political boundaries for the Granada Community Services District https://granada.ca.gov and the Midcoast Community Council https://midcoastcommunitycouncil.org and found a need to display some GeoJSON files on a map and export that as a PNG. I asked GPT-5.6-Sol for suggestions of tools and it proactively built one. After some iterations https://tools.simonwillison.net/colophon geojson.html using Claude Code for web and Fable 5.1 we got to this finished tool. As for the GeoJSON.. it turns out if you ask ChatGPT Work to provide boundaries for almost anything it will churn away extracting and combining files from different Government data sources and build exactly what you need. I got this polygon https://gist.github.com/simonw/27d243c9d1cb5d9047fff7360dd49d3c from: I want a polygon that represents the exact boundary of the El Granada GCSD And this one https://gist.github.com/simonw/b51f9e0190a13932ac64a0cb407a709d from: Get me a GeoJSON file for the boundary or boundaries if that makes sense for the MCC - Midcoast Community Council - that operates near Half Moon Bay CA Here's a link https://tools.simonwillison.net/geojson url=https%3A%2F%2Fgist.github.com%2Fsimonw%2Fb51f9e0190a13932ac64a0cb407a709d&color=%23028FC3&opacity=50&url=https%3A%2F%2Fgist.github.com%2Fsimonw%2F27d243c9d1cb5d9047fff7360dd49d3c&color=%23E4572E&opacity=50&preset=map&resolution=2&lat=37.52640&lng=-122.48297&zoom=13 that displays both of them at the same time on the new GeoJSON map viewing tool. Tags: geospatial https://simonwillison.net/tags/geospatial , tools https://simonwillison.net/tags/tools , geojson https://simonwillison.net/tags/geojson