Understanding Vessel Positions in Skylight

The Vessels Positions Layer displays the most recent position of every vessel broadcasting AIS globally. It is designed to provide analysts with at-a-glance picture of vessel activity across their areas of interest and key contextual information to take action on Events.

Data Source: AIS

The vessel data layer is powered by AIS (Automatic Identification System) data. AIS is a maritime broadcasting system in which vessels transmit their position, speed, course, heading, and navigational status at regular intervals. AIS messages also carry identity information including the vessel name, MMSI, IMO number, flag state, and vessel type.

Skylight ingests a near-real-time AIS feed and processes it to display each vessel's most recent known position on the map, as well as its historical track over time. This same AIS data is used for event detection — identifying patterns such as fishing activity and rendezvous. 
 

Vessel Visualization Options

The Visualization Settings panel allows users to customize how vessel icons appear on the map. Under the Vessels section, the following color-coding options are available:

• MMSI — Colors vessels by their unique Maritime Mobile Service Identity number. Useful when monitoring several specific vessels simultaneously, making it easy to distinguish one from another at a glance.

• Vessel Type — Colors vessels by category (e.g., cargo, tanker, fishing, passenger). Ideal for quickly identifying the composition of traffic in an area — for instance, spotting fishing vessels operating near a shipping lane.

• Flag — Colors vessels by their registered flag state. Valuable for jurisdictional awareness, such as identifying foreign-flagged vessels operating within an EEZ.

• Latest Update — Colors vessels by how recently their position was reported. Helps analysts assess data freshness and identify vessels whose AIS signal may be going stale.

• Speed Over Ground — Colors vessels by their current speed. Useful for distinguishing between anchored or drifting vessels and those actively transiting or maneuvering.

• Recent Events — Colors vessels based on whether Skylight has recently detected behavioral events associated with them. A quick way to prioritize attention toward vessels that have triggered alerts.

• Time of Day — Colors vessels based on the time their last position was reported. Helpful for understanding patterns of activity relative to daylight hours — for example, identifying vessels that are only active at night.

Track Visualization Options

When viewing a vessel's historical track, the Track Options section offers a separate set of color-coding choices:

• MMSI — Distinguishes tracks by vessel identity when viewing multiple tracks on the map at once.

• Position Age — Colors track segments by how old each position is, creating a visual timeline from oldest to most recent. Useful for understanding the sequence and recency of movements.

• Speed Over Ground — Colors track segments by vessel speed at each point. Reveals where a vessel slowed down, stopped, or accelerated — key for identifying potential fishing activity, loitering, or port calls.

• Time of Day — Colors segments based on when they occurred during the day. Helps reveal whether a behavior happened at night or during daylight.

Combining Options for Deeper Analysis

These visualization settings can be used in combination across the vessel and track layers. For example, an analyst might color vessels by Flag to identify foreign-flagged fishing vessels in a national EEZ, then select a vessel of interest and view its track colored by Time of day to see when it was fishing. Alternatively, coloring vessels by Speed Over Ground can highlight slow-moving vessels that may be engaged in fishing or loitering, and switching the track view to Time of Day can reveal whether that activity occurred under cover of darkness.