Methodology and data sources

Register Atlas is built from the National Park Service records of the National Register of Historic Places. The site is rebuilt every Saturday, after the Park Service posts its weekly list of new listings and removals. Data refreshed October 17, 2026.

Sources

• The National Register spatial data is the Park Service's map layer. It gives most listings their name, address, county, type and coordinates.
• The National Register office's spreadsheet of listed properties, from the same page, is the source of record. It supplies every listing date and landmark designation, why each place was listed, whether its significance is local, state or national, and other names it has gone by. For a listing the map layer lacks, it also supplies the name, address, town, county and category.
• The weekly list adds new listings, boundary changes and removals as they are announced.
• Nomination forms and photographs are linked from the Park Service's NPGallery and from the National Archives. The nomination form is the document that argues why a place matters, and it is usually the best description of it.
• Wikidata supplies construction dates, architects and styles where editors have recorded them. It also supplies the map point for a listing the map layer does not place, where Wikidata records one. Wikipedia supplies the short summaries, which are credited on the page and used under CC BY-SA.
• Photographs come from Wikimedia Commons under the license shown with each one. Drawings and survey records come from the Historic American Buildings Survey at the Library of Congress.
• Wikipedia view counts come from the Wikimedia pageviews API.

How the records are joined

Every source carries the register's reference number, and that number is the key for every join on the site. A listing is never matched by name alone. National Historic Landmarks have a full record. Other listings appear as a row in their county, and the row opens to show everything held for that place.

The site holds 101,425 listings, against 100,793 listed properties in the May 22, 2026 edition of the spreadsheet. Of these, 72,673 come from the map layer and 28,752 come from the spreadsheet alone, because the map layer does not carry them. A listing from the spreadsheet appears as a row on its county page like any other.

Coordinates come from the map layer first and from Wikidata second, matched on the reference number. Wikidata supplies the map point for 17,784 listings. A point that falls outside the listing's own state is not used. 10,987 listings from the spreadsheet have no point in either source, so they appear in their county's list with no map pin and no distance. The site never places a listing by looking up its address or by putting it at the center of its town or county.

The spreadsheet marks 5,693 listings as having a restricted address. The Park Service withholds these locations on purpose, to protect archaeological sites and other sensitive places. Their rows show the name, county, listing date and category. The site publishes no address and no coordinates for them from any source, Wikidata included.

Listing dates and National Historic Landmark status come from the National Register office's own spreadsheet. A listing it carries counts as a landmark only when the spreadsheet gives it a landmark designation date. A building is sometimes designated under a newer reference number than its first listing, and only that newer record is marked as the landmark. Listings missing from the spreadsheet keep the landmark flag from the Park Service layer or Wikidata.

What the data cannot tell you

• A listing with no map point is still on the register. It is missing from maps and nearby lists only because no source places it, or because its location is withheld.
• The spreadsheet is reissued a few times a year, so a place listed since its latest edition appears on the weekly list before it has a row here.
• A listing records that a place was found significant on a given date. It says nothing about whether the place is open to visitors, and most listed buildings are private property.
• Construction dates, architects and styles depend on what Wikidata editors have entered, so many listings have none.
• Some Wikipedia summaries describe the district or neighborhood a building stands in, because that is the article the listing is linked to.
• The reason for listing is coded by the register in broad areas such as architecture, commerce or transportation. The nomination form holds the full argument.

The files behind the site are free to download from the open data page.