Hidden America
Every place on the National Register, on your phone. If something isn't working, or a listing needs correcting, there's a real person at the other end of the links below.
Why is there nothing on my map?
Most likely you're outside the United States. The National Register is a US register, so the app covers the fifty states and the territories and nowhere else. It can happen inside the country too — a great deal of America is a long way from the nearest listed place. Either way, use Browse, which is where the app opens: every state, then every city, then every listing.
Does it work without an internet connection?
The map, the search, the browsing and every listing's federal record are on the device and need no signal at all. Two things do need a connection: the archival photographs, which come from the Library of Congress as you open a place, and the written history, which is generated on request.
What is the API key for, and do I need one?
The written history, Then & Now and building identification are generated by Claude, and they run on your own Anthropic API key rather than a subscription to us. Without a key the app is a complete offline atlas of the National Register — map, search, browse, the record, the photographs, the passport. With one, it also explains what you are looking at. Keys come from console.anthropic.com; you pay Anthropic directly for what you use, and nothing to us.
Where is my API key stored?
In the iOS keychain on your device. It is sent to api.anthropic.com and nowhere else — not to us, not to any other service. Remove it any time in Settings.
Why does it want my location?
To show what is around you and to sort places by how far you would have to walk. That happens on the device. The one time your coordinates leave the phone is when you use the camera to identify a building, because the guide has to know where you are standing and which way you are pointing to work out what you are looking at. Decline the permission and everything else still works — browse and search do not need it.
How accurate is identifying a building?
Treat it as a lead, not a verdict. It reasons from the photograph, your compass bearing and the listings lying in that direction, and it shows a confidence with every answer. It is built to say likely rather than to sound certain, and to answer that none of them match when none of them do. If it names a building, check it against the record before repeating it.
A listing is wrong, or one I know is missing.
The data is the National Park Service's, not ours — we ship what they publish, so corrections have to reach them. Two gaps are worth knowing about: the Service withholds restricted and sensitive archaeological sites, which is deliberate and right, and 171 listings arrive with no city or state recorded, so they appear on the map and in search but under no state. Tell us anyway; if it is ours, we will fix it.
Where do the styles, eras and themes come from?
Not from the federal record, which carries a name, a type and a location and little else. Places in San Francisco, Washington and New York were written up by hand. Everywhere else the guide classifies what is on your screen when you use those filters, once, and remembers it. The app always shows which of the two you are reading.
What is a National Historic Landmark?
A listing singled out as nationally significant — 2,429 of the 90,180 places here. They carry a star, and they are what the map draws when you zoom out far enough that showing everything would be meaningless.
Where is my passport stored?
On your device and nowhere else. Visits, notes, saved places and what you took away from each place never leave the phone. There is no account and nothing syncs, so deleting the app deletes them.
Can I use the photographs?
Rights vary item by item at the Library of Congress, and a great many items are free to use and reuse. Every photograph in the app links to its page at loc.gov — check there before republishing one.
Write to hello@ptk-studio.com. For a bug, your iPhone model and iOS version and what you were doing when it happened is enough to start. For a listing that looks wrong, its reference number — shown under The federal record on every place — saves us both some time.