In a post dated 1st September 2026, developer Simon Willison described building a web-based GeoJSON map viewer while helping someone named Natalie gather maps of local political boundaries for the Granada Community Services District and the Midcoast Community Council, which operates near Half Moon Bay, California. Willison wrote that he needed to display GeoJSON files on a map and export the result as a PNG image. According to the post, he asked a tool referred to as GPT-5.6-Sol for suggestions, and it 'proactively built one.' After iterations using Claude Code for web and a tool referenced as Fable 5.1, he arrived at a finished viewer. Willison also stated that asking ChatGPT Work to provide boundaries for 'almost anything' resulted in it extracting and combining files from different government data sources to produce the needed GeoJSON. He gave example prompts requesting a polygon for the El Granada GCSD boundary and a GeoJSON file for the Midcoast Community Council boundaries, and linked to the tool displaying both at once. The account is based on a single blog post by Willison and describes tool names and versions not independently confirmed here.
What it means for you
A well-known developer showed that AI coding assistants can build a small, single-purpose web tool from a plain-English request, and that AI chatbots can assemble map boundary data from public government sources. It's a concrete example of using AI to solve a niche problem quickly rather than hunting for existing software.
Try this
If you occasionally need a small, specific utility (a map viewer, a file converter, a simple form), try describing exactly what you want to an AI coding tool and see if it builds a working version before you go looking for paid software.
Who should care
People who work with geographic or boundary data, and anyone comfortable enough to describe a small tool to an AI and run the result.
Skip this if
You don't work with maps or GeoJSON files and have no interest in building your own small web tools.
Sources: Simon Willison — read the original