Explainer
What is AIS and how does its API actually work?
If you work with vessels you have heard of AIS. Here is how the data gets from a ship's transponder to your screen.
AIS stands for Automatic Identification System. Every vessel above a certain size is required to broadcast a short message over VHF radio every few seconds: who they are, where they are, where they are going, and how fast.
From transponder to screen
- The ship’s AIS transponder emits a radio message.
- A receiver — either on shore, on another ship, or on a satellite — picks up the message.
- The receiver forwards the message to an aggregator (AISHub, MarineTraffic, Spire, etc.).
- The aggregator exposes an API that your application reads from.
The gap between step 3 and step 4 is where most integration headaches live.
What the API actually returns
A typical AIS API response is a JSON document with fields like mmsi, lat, lon, sog (speed over ground), cog (course over ground), heading, nav_status, and timestamp.
{
"mmsi": 259000000,
"lat": 57.70,
"lon": 11.97,
"sog": 12.4,
"cog": 182,
"timestamp": "2026-04-12T08:14:00Z"
}That one object, streamed for every vessel in the world, is the raw material for route planning, port logistics, emissions reporting, and much of maritime research.
The next explainer covers how to filter that stream without bankrupting yourself in API calls.