Where this data comes from

Every position on this site is traceable to a named public feed. We do not generate, estimate, interpolate or infer vessel positions. If a feed stops, the affected pages say so rather than showing you the last thing we saw as though it were current.

Current feeds

We run three. AISStream.io is the primary feed — a worldwide stream fed by a community network of shore-based receivers. Digitraffic (Fintraffic) is the global-stream fallback: an official government feed covering Finland and the surrounding Baltic, used when the global stream drops so the map keeps working somewhere rather than nowhere. Kystverket(Norwegian Coastal Administration) is a regional feed covering Norwegian coastal waters under the NLOD open licence. Every position on the site names which feed it came from.

What this coverage actually means

For a practical explanation of the map's observed-traffic layer and how to check a missing vessel, start with where our AIS coverage reaches.

AIS is a VHF radio system, and VHF is line-of-sight. A shore station hears a vessel out to roughly 40–60 nautical miles in good conditions, sometimes further, often less. Everything on this site comes from shore-based receivers, so:

• Coastal waters are well covered; open ocean is not covered at all.A ship that leaves the receiver network does not disappear because something went wrong. It is simply out of radio range. A vessel that vanishes mid-Atlantic has not “gone dark”.
• “Global” describes the receiver network, not our ability to see every ship.The network is dense around Europe, North America and East Asia, thinner along other coasts, and effectively absent in mid-ocean. Reach is worldwide; completeness is not, and we do not claim it.
• Coverage is uneven and it moves. Receivers are run by volunteers. One going offline takes a stretch of coast with it, and a new one adds coverage that was not there last week. Gaps are about who is listening, not about who is sailing.
• Some vessel classes are filtered upstream. The Finnish provider removes fishing vessels before publishing, so their absence from that feed is a property of the feed, not evidence about the sea.

Satellite AIS

Services with genuine ocean-wide coverage buy satellite AIS, which is licensed commercial data. We do not use it, and nothing on this site should be read as though we do. Our reach is global; our coverage stops at the horizon of the nearest shore receiver.

Freshness

The live map reads the upstream feed directly and refreshes about once a minute, falling back to Digitraffic if the global stream is unavailable. Vessel pages are backed by a store that updates every twenty minutes, so a vessel page can lag the map. Both surfaces show the age of the position they are displaying — trust the timestamp, not the fact that a dot exists.

Port activity index

The port activity index counts vessels in the AISStream.io snapshot within 10 nautical miles of each port's approximate reference point, once per UTC day from 12:00 UTC. It measures what our receivers can hear, so it moves with receiver coverage as well as with shipping. Days without a sample stay empty; nothing is backfilled. The derived counts are published under CC BY 4.0 as CSV and JSON.

Corrections

If something here is wrong, tell us atcontact@marineactivity.com. Note that we republish upstream data as received: if a vessel is transmitting an incorrect name, destination or position, the correction belongs with the vessel's operator or the feed provider, though we are glad to be told about it.