Cartographic timeline
Five David Rumsey map series + two Library of Congress Sanborn fire-insurance sheets, mined via Gemini 2.5 Pro vision OCR over May 28-29, 2026. Each map captures a moment the prior one didn't.
Sources: David Rumsey Map Collection (1854 Dripps, 1866 Johnson, 1874 Fulton Section 10, 1889 Standard World Atlas, 1897 Rand-McNally) and Library of Congress Sanborn Map Collection (sanborn05791_018, 1906 Vol 6, Sheets 65 + 74). OCR via Gemini 2.5 Pro on Vertex AI; cost ~$0.20 per map. Image files in public/findings/maps/.