Vision, hearing, and, to some extent, olfaction provide information about a traveler’s current position and orientation even when the traveler has no prior estimate, such as might be gained from self-movement. If the traveler has an external or internal map of the environment, visual, auditory, and olfactory information from known locations (landmarks) within the map can be used to determine current position and orientation, using triangulation (based on bearings), trilateration (based on distances), a combination of the two, and other techniques (Gallistel, 1990).