Simon Willison runs a 27-minute GPT-6 Astra agent task to generate OSM-based running routes
Simon Willison · rss · 2026-09-13
Simon Willison used ChatGPT Work with GPT-6 Astra (Max) to generate 5K and 10K looping running routes from his home using OpenStreetMap data. The agent worked for 27 minutes and delivered exactly what he asked: an embedded visualization plus downloadable GPX and GeoJSON files.
- The model's self-described workflow: Nominatim for geocoding, Overpass to download local OSM roads and trails, then local loop calculation.
- Rendering used the visualize skill, producing an HTML file with embedded D3 sourced from allow-listed CDNs; the CSP only permits cdnjs.cloudflare.com, esm.sh, cdn.jsdelivr.net, unpkg.com and a few font origins—others fail silently.
- Route geometry lives in a <script type="application/"> element.
- His main criticism: the actual code the agent ran was not visible in the ChatGPT UI, a transparency anti-feature.
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