AIS vs GPS: What's the Difference?
AIS vs GPS: What's the Difference?
If you work anywhere near shipping, you will hear "AIS" and "GPS" used almost interchangeably. They are not the same thing. The short answer to AIS vs GPS is this: GPS tells a ship where it is, and AIS tells everyone else. One is a positioning system; the other is a communication system that broadcasts that position, along with the ship's identity and movement, to every station in range.
This guide explains how each works, where they overlap, and why modern vessel location tracking depends on both.
What is GPS tracking?
GPS (Global Positioning System) is a satellite navigation system operated by the United States. A constellation of satellites transmits precise timing signals. A GPS receiver on a ship, a phone or a truck listens to at least four of them and calculates its own latitude, longitude and altitude.
The key point is that GPS is receive-only. A GPS receiver works out its position but does not transmit it anywhere. On its own, GPS tracking means the device knows where it is, and nobody else does.
To turn GPS into a tracking service, you need a second link: a cellular modem, a satellite transmitter or a radio that sends the position to someone else. That is exactly the gap AIS fills at sea.
What is AIS tracking?
AIS (Automatic Identification System) is a maritime radio system. Every few seconds, a ship's AIS transponder broadcasts a short digital message on two dedicated VHF channels (161.975 MHz and 162.025 MHz). Other ships, coast stations and AIS satellites receive those messages.
Each AIS message carries:
- Identity: the ship's MMSI, name, call sign and IMO number
- Position: latitude and longitude, usually taken from the ship's GPS receiver
- Movement: speed over ground, course over ground, heading and rate of turn
- Voyage details: destination, ETA, draught and navigational status
AIS was designed for collision avoidance, so that a bridge officer could see who is approaching and where they are heading, even in fog or at night. Today the same broadcasts power AIS vessel tracking platforms that show ships on a live map worldwide.
Under the SOLAS Convention, AIS is mandatory for ships of 300 gross tonnage and above on international voyages, cargo ships of 500 GT and above on domestic voyages, and all passenger ships regardless of size.
AIS vs GPS: the key differences
| GPS | AIS | |
|---|---|---|
| What it is | Satellite positioning system | VHF radio broadcast system |
| Direction | Receive-only | Transmits and receives |
| What it provides | The receiver's own position and time | Identity, position, speed, course and voyage data |
| Who sees the data | Only the device itself | Every AIS station in range, plus satellites |
| Main purpose | Navigation | Collision avoidance and maritime domain awareness |
| Who uses it | Ships, aircraft, vehicles, phones | Ships, coast stations, port authorities, tracking platforms |
How AIS and GPS work together
The AIS vs GPS comparison is a little misleading, because on most ships they are partners rather than rivals. The AIS transponder is connected to a position source, almost always a GPS (or wider GNSS) receiver. GPS supplies the coordinates and the time; AIS packages them with the vessel's identity and broadcasts them.
That is why AIS tracking is so useful for anyone off the ship. A GPS fix sitting inside a receiver helps only the crew. The same fix broadcast over AIS lets a port agent, a charterer or a fleet manager see the vessel's location in near real time.
AIS vs GPS tracking: which should you use?
It depends on what you are tracking and why.
- For merchant ships covered by the SOLAS carriage rules, AIS is already on board and transmitting. AIS vessel tracking is the natural choice: no extra hardware, no cooperation from the operator needed, and coverage of almost the entire commercial fleet.
- For your own small craft, barges or assets that do not carry AIS, a dedicated GPS tracking unit with a cellular or satellite link can report position privately to your own systems.
- For security-sensitive operations, GPS tracking over a private link keeps the position out of public view, while AIS broadcasts openly to anyone listening.
Most commercial teams end up combining both: AIS for the wider picture of who is where, and private GPS feeds where they need it.
Limitations to keep in mind
Neither system is perfect. GPS signals can be jammed or spoofed, which in turn corrupts the position an AIS transponder broadcasts. AIS can be switched off, and vessels sometimes go "dark" in sensitive waters. Terrestrial AIS also has limited range, typically 20 to 40 nautical miles from a shore station, which is why satellite AIS is used to fill the gaps over open ocean. Good vessel location tracking means reading the data critically, not just plotting dots.
Track vessels with Navtrac
Navtrac turns raw AIS broadcasts into a live maritime intelligence picture. You can follow vessels worldwide on an interactive map, monitor ports and traffic in real time, and use predictive analytics to make faster, data-driven decisions about your fleet and your cargo.
Want to see AIS vessel tracking in action? Explore Navtrac and follow any ship on the live map.