The GIS Trigger Service is a background service whose job is to monitor the ship's current position and launch predefined actions when certain geographical boundaries are crossed.
This service listens to the system's reference Latitude and Longitude data streams in order to determine the ships position. Disabling ACQ or not specifying a Lat/Lon source in CFE will effectively render this service useless.
Actions are not launched immediately when a boundary is crossed. Instead the service waits until the vessel is 0.25 nautical miles past the boundary before firing the actions. This is to ensure that the ship is indeed past the point and will not traverse back and forth (eg moving slowly in heavy seas or is riding the line, etc) causing the action to be launched repeatedly.
This buffer distance is adjustable, you can change the GISTrigger.BoundaryCrossingMargin variable in the services config file if you feel this number is to high or to low.
See also: GIS Triggers