Old map viewers already exist: the National Library of Scotland's side-by-side viewer, Old Maps Online, the USGS historical topo explorer. They are wonderful and they leave all the work to you: you have to know what to look for. Vanished Places does the looking. It compares the 1900 map with today's map automatically, finds what disappeared near you (a buried river, a lost railway, a village under an estate) and turns each one into a short walk that ends with you standing on the exact spot.
The data it runs on
Old maps: free georeferenced historic map layers: the National Library of Scotland's Ordnance Survey six-inch and 25-inch maps of Great Britain (about 1840s to 1950s, served as tiles), and the USGS Historical Topographic Map Collection for the United States (scanned GeoTIFFs from the 1880s onward).
Today: OpenStreetMap, via a vector tile extract or the Overpass API: water, railways, buildings, paths, land use and names.
How it is compared: a vision segmentation model traces water, rail, buildings and ponds on the old tiles; the traces are compared with OSM features in the same place. Old features with no modern match become candidates, and names (Mill Lane, Windmill Roundabout) are matched as clues.
Limits and fallback: georeferencing can be off by 10 to 50 m, so arrival uses a generous radius; outside Britain and the US, free historic coverage is patchy, so the app falls back to Wikidata "former" places and local history submissions. The district in this demo is a fictional sample built from typical features; the world places in the collection are real.
1. The mission
Give everyone the ghost layer of their own neighbourhood. Every street was something else once. Knowing that a river runs under your road changes how you walk down it.
2. Why people can't resist it
Secret knowledge. "There's a river under the supermarket car park" is the best fact you'll tell anyone this week.
The swipe. Dragging 1900 across today is pure magic, every time.
A walk with a destination. Standing on the exact spot, with the old map in your hand, is a small pilgrimage you can collect.
3. How it works for real
Tiles: fetch old map tiles (NLS, USGS) and today's OSM features for a 1 km radius.
Trace: a vision model (Gemini or a Claude model via OpenRouter, or a fine-tuned segmentation model for map symbols) labels water, rail, buildings, pits and mills on the old tiles.
Diff: geometry code matches old features to OSM; unmatched ones become vanished place candidates, scored by size and how dramatic the change is.
Story: a frontier LLM writes a 120 word story for each from the map evidence plus open sources (Wikipedia, local history pages, census years), with sources shown and uncertain claims marked.
Walk: phone GPS guides you to the spot; arrival within 25 m stamps your collection and makes the before and after card.
4. Cost per use
Mostly map processing; cheap. Tracing a 1 km area is done once and shared by everyone there: about $0.05 per area. Stories cost about $0.01 each. Per user, close to nothing.
Free: everything within 1 km of you. Explorer ($3 a month): any place on Earth, guided multi-stop walks, print-quality before and after posters, and offline maps.
5. Growth loop
Before and after cards are made for local Facebook groups and neighbourhood chats ("I'm standing where the mill pond was"). Local historians add stories and corrections, and each added story pulls their followers in. Schools use walks for local history lessons.
6. Risks and guardrails
Trespass and safety: targets on private land, railways or water are moved to the nearest public point, and the app says so.
Accuracy: every story shows its sources and the map dates. "Probably" means probably.
Licences: NLS and USGS terms are followed and credited; OSM is credited as "OpenStreetMap contributors".
Sensitive history: clearances, slums and disasters are told with care, and residents can add their own memories.
7. MVP build order
Swipe viewer with NLS tiles over OSM for one city.
Hand-picked list of 20 vanished places there, with stories, to test the walk.
Walk to the spot with arrival check and the before and after card.
Automatic tracing and diff for water and rail first.
Collection, sharing, then a second country with USGS maps.