1. A method for correlating the positional data of a intruder in an interrogation-based air traffic surveillance system and the positional data of a target in a Global Positioning System-based air traffic surveillance system, the method comprising the steps of: receiving a GPS-based surveillance broadcast from a target including positional data; correlating the target positional data with positional data from one or more entries in an intruder file, each entry associated with one or more intruders; and displaying a single icon on a display terminal if the correlation process results in a determination that the target and one of the intruders are the same aircraft.