Model zone data and model subzone data is employed to simplify calculations for determining where and/or when a boundary crossing event has occurred. A system for detecting a boundary crossing event employs a memory and a processor. The processor in one embodiment is configured by the memory to perform the steps of sensing current position; comparing the sensed current position to model zone data to determine presence within a geometric figure constructed around a boundary crossing point; comparing the sensed current position to model subzone data to determine presence within a first portion of the geometric figure; comparing the sensed current position to model subzone data to determine presence within a second portion of the geometric figure; and detecting a boundary crossing event as a result of movement from the first portion of the geometric figure to the second portion of the geometric figure.