The Automatic Identification System (AIS) is an electronic system enabling vessels to send localization messages. Those messages are used for several uses such as fleet monitoring, traffic control or boarding prevention. The messages sent contain errors, falsifications and undergo spoofing due to the unsecured channel of transmission, and that weakens the whole system and the safety of navigation. This paper introduces the methods for the integrity assessment of messages and the discovery of anomalous data, particularly based on spatial information, which is the cornerstone of AIS messages. This will lead to the determination of non-genuine messages and the highlighting of falsifiers, with the objectives to discover the falsifications, point out the falsifiers, remove the falsified messages from the following studies and thus improve the effectiveness of the system.