Compare geographic shapes on one map. Paste GeoJSON, set colors and opacity for each overlay, and export a map image. Simon Willison built the initial tool with GPT-5.6 Sol and refined it with Claude Code. Explore the live viewer and creator screenshot.
Created by Simon Willison
Built with ChatGPT · GPT-5.6 Sol
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Source checked September 27, 2026Original creator article explicitly credits initial GPT-5.6 Sol implementation and later Claude Code refinements. Browser verification on September 27 loaded example data and rendered two styled shapes, a route and point over OpenStreetMap. Creator-hosted thumbnail visually inspected and matches the live interface. No matching project in prior research/lib search or current 93 hosted entries.
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