How MarineTraffic Tracks Ships and How Current the Data Is

MarineTraffic tracks ships primarily through AIS (Automatic Identification System) signals that vessels broadcast, then plots those positions on a near real-time map. The data is usually current within minutes in well-covered coastal areas, but it can be delayed or missing where AIS reception is weak — for example, mid-ocean or in regions with sparse receiver coverage. So the map is best understood as "near real time," not a guaranteed live feed for every vessel everywhere.

Where the position data comes from

AIS is a radio system that certain ships use to transmit their identity and location. MarineTraffic collects those transmissions and turns them into map positions and vessel details.

The site describes its coverage as a global ship tracking service with a live ships map, and it maintains a database of more than 550,000 active and decommissioned vessels. That database is what lets you search for a specific ship and view vessel details and photos, not just watch dots move on a map.

What AIS actually carries

An AIS message typically includes:

• A vessel identifier (such as MMSI or IMO number)
• Position (latitude and longitude)
• Course and speed over ground
• Heading and navigational status
• Timestamp of the transmission

Because these fields come from the vessel's own equipment, the accuracy of what you see depends on the transmitter working correctly and on a receiver actually catching the signal.

How signals reach the map

AIS is a short-range radio signal, so getting it onto a global map requires two layers of reception.

1. Shore-based receivers

Coastal stations pick up AIS transmissions from ships within radio range of land. This is why coverage is densest near ports, coastlines, and busy shipping lanes. In these areas, positions tend to refresh frequently and appear close to real time.

2. Satellite reception

Satellites can receive AIS from vessels beyond the range of shore stations, which extends coverage into open ocean. Satellite reception, however, is not continuous for a given ship — a satellite only "sees" a vessel when its orbit passes overhead, so updates in remote areas can be spaced further apart.

The practical result: the same ship may update every few minutes near a coast and much less often in the middle of an ocean.

How current the data really is

"Near real time" is the honest description. What you see is the last position MarineTraffic received, not necessarily where the ship is at this exact second.

Two things follow from this. First, a position on the map always reflects a past moment, so treat it as the latest known location rather than a live coordinate. Second, gaps are normal, not a sign that something is wrong with the site — they usually reflect reception limits or the vessel's own equipment.

Why some ships or areas show gaps

• Reception limits. AIS is radio-based, so distance from a receiver matters. Areas far from shore stations and outside satellite passes will have thinner coverage.
• Equipment and configuration. If a vessel's AIS is off, faulty, or misconfigured, its data won't appear or may be incomplete.
• Regulation. Not every vessel is required to carry or operate AIS, so some ships simply aren't represented.
• Congestion and processing. In very busy areas, high volumes of transmissions can affect how quickly positions refresh.

How to use the map with the right expectations

1. Search for a specific vessel using the ships database if you want details on a known ship rather than browsing the map.
2. Check the timestamp on a position before relying on it — that tells you how current the data actually is.
3. Read coastal positions as fresher than open-ocean ones, and expect wider gaps offshore.
4. Treat missing data as a coverage or equipment question first, before assuming anything about the vessel's activity.

In short, MarineTraffic gives you a near real-time picture built from AIS signals collected by shore stations and satellites. It is highly current in well-covered coastal waters and less so in remote areas, so the timestamp and location context matter as much as the dot on the map.