To establish situation awareness during air defence surveillance missions, track level data from sensors and additional data sources are combined to form the air picture for the region under surveillance. Typically, compilation of the air picture and the C4ISR activities that it supports, namely real-time surveillance, fighter control and situation and threat assessment at the tactical level, and mission planning and intelligence collection at the theatre level, are all performed manually by defence and intelligence operators. To assist operators with compilation of the air picture and its subsequent applications, it is desirable to introduce automation to the information processing required for these activities. To accomplish this requires the use of the contextual information in the surveillance region to extract descriptive (symbolic) information about the behaviour of each detected air target from the positional and kinematic data in its state estimate. Since much of the contextual information exists in the form of entities and regions that can be modeled geometrically, it is possible to perform the information extraction using geometric criteria. In this paper, this philosophy is followed to produce such a set of geometric criteria which can be used to extract information that can be conveniently represented as predicates. First the choice of the criteria is motivated by an examination of the nature of the information which is to be extracted, before describing the mathematical details required for determining that the criteria are met. Several examples are also given to illustrate the methodology for using the criteria. Finally, the future directions for the further development, test and evaluation of the methodology are briefly discussed.