This tracking map is created from real-time AIS (Automatic Identification System) signals. AIS is a real-time system that all commercial ships use, including cruise ships. Most AIS information is transmitted via VHF, therefore, ships positions may only be available at or near a port having AIS receivers. For that reason, unless a ship has long-range AIS, ship information may not be available on the high seas. For more information on how AIS works, see my AIS tutorial.