1. A system for relating a passive sensor to a geographic environment, the passive sensor being operable to sense an image of the geographic environment, comprising: storage circuitry for storing map data having predetermined levels of complexity to relate with the image and representative of the geographic environment; and process circuitry coupled to said storage circuitry and to the passive sensor and operable to: extract at least one image range discontinuity from the image; generate at least one map range discontinuity from said map data; and relate said at least one said extracted image range discontinuity to said at least one said generated map range discontinuity with said predetermined levels of complexity, such that the passive sensor is related to the geographic environment.