Glossary
Automatic Identification System (AIS)
AIS is the VHF broadcast system whose position and voyage messages form the raw material for nearly every marine-transportation dataset cataloged here. Live feeds stream decoded AIS worldwide via AISStream.io, US Coast Guard broadcasts are republished as bulk CSV and GeoParquet by MarineCadastre, and EMODnet turns AIS into 1x1 km density rasters.
What is Automatic Identification System?
Ships broadcast their identity, position, course and voyage details over VHF several times a minute; anyone with a receiver - coastal station or satellite - can decode the messages. That reception record is what datasets package.
Three forms appear in this slice. AISStream.io's Live AIS WebSocket API streams 'decoded AIS vessel positions, static voyage data and other AIS message types worldwide'. MarineCadastre's AIS Vessel Traffic Data republishes 'US Coast Guard Nationwide AIS broadcast point records' as bulk CSV and GeoParquet. And EMODnet's Vessel Density Maps are 'AIS-derived vessel density rasters for all EU waters at 1x1 km'.
Why does AIS matter when choosing a dataset?
Every downstream marine product inherits AIS physics. Receivers sit on coasts and satellites, so coverage tracks receiver placement - gaps offshore produce the dark-vessel problem where ships simply stop appearing, which no analytics can conjure back.
Product type follows message type. Position reports give tracks; static voyage data gives ship characteristics keyed by MMSI; aggregated reception gives density rasters. Buyers should therefore match source to question - live operations need the WebSocket feed, historical traffic analysis needs Coast Guard point records or EMODnet grids, and vessel-profile enrichment needs the staticvoyagedata layer each provider exposes differently.
How do you evaluate AIS-based data in a source?
- Trace the reception chain. Confirm whether records come from live decode (AISStream), official republishing (MarineCadastre of Coast Guard Nationwide AIS) or derived aggregation (EMODnet).
- Check format fit. Bulk CSV and GeoParquet suit archive analysis; WebSocket streams suit operations; 1x1 km rasters suit heatmapping only.
- Mind identifier integrity. MMSI keys position and voyage messages together - validate before joining across providers.
- Quantify coverage honestly. Ask how receiver and satellite footprint limits manifest as dark-vessel gaps in your waters of interest.
Related terms
- ais-position-report - the core positional message type.
- ais-websocket-stream - the live delivery channel.
- dark-vessel - ships absent from reception, the coverage failure mode.
- mmsi - the vessel identity key across AIS records.
- vessel-density-map - the aggregated raster form.
Sector hub: marine-transportation data.
Frequently asked questions
Where does marine traffic data come from?
Mostly AIS reception. Live positions stream from decoded AIS messages worldwide via AISStream.io's WebSocket API, while US Coast Guard Nationwide AIS broadcasts are republished as bulk CSV and GeoParquet.
What resolution do AIS density maps use?
EMODnet's Vessel Density Maps provide AIS-derived vessel density rasters covering all EU waters at 1x1 km grid cells.
Datasets containing this field
Datasets containing Automatic Identification System (AIS)
6 datasets carry automatic identification system (ais) in the catalog. Open one, count the fields, judge for yourself.
AISStream.io Live AIS WebSocket API
BarentsWatch Open AIS API (Norwegian Coastal Administration)
Data.gov Maritime Collection
EMODnet Vessel Density Maps (EU Waters)
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