At the highest level, SAIF distinguishes between representations of real world phenomena and representations of the space and time in which (during which) they exist. Representations of real world phenomena are referred to as geographic objects. Roads, forest stands, geological strata, oil spills, and temperature readings are examples. Such objects may have various relationships to one another, including spatial and temporal relationships. Two streets intersect. An oil spill occurred durig a storm.
The position of each phenomenon in space is represented by a spatial object. If both space and time are considered, the position of the phenomenon is represented by a spatiotemporal object. Thus, if a particular type of geographic object is considered as spatial in nature, it will have a corresponding spatial object. If it is considered as spatiotemporal in nature, it will have a corresponding spatiotemporal object.
SAIF provides a large number of spatial and spatiotemporal constructs, many of which may be subclassed by users to define new classes of direct utility to them. Detailed, more technical textual and graphic descriptions of the classes below may be found in Chapter 3.