FAQ

Where does your tide data come from?

NOAA Tides & Currents (CO-OPS). We hit the NOAA REST API on a five-minute poll for every station within 5 nautical miles of a working harbor in our index. We do not republish — we cache and reformat as JSON, with the upstream station ID and timestamp preserved on every record.

What's the AIS data source?

We ingest the public T-AIS feed and a commercial AIS aggregator for fill-in coverage on stations the public feed misses. AIS is best-effort: small craft without transponders are by definition not in the dataset.

Can I use this for navigation?

No. Coastline is a data publishing project for analysts, researchers, and journalists. It is not a navigation aid and must not be used as one. For navigation, use NOAA's official charts and your vessel's certified equipment.

Why thirty-eight harbors and not, say, every port?

We started with the harbors that had at least one NOAA tide station within five nautical miles AND a working commercial fishing or ferry fleet of at least ten vessels. As funding allows, we'll add stations. The coverage map on the home page is the current ground truth.