The topographic map revealed in the olfactory system differs in quality from the orderly representation inherent in the retinotopic, tonotopic, or somatotopic sensory maps. Olfactory neurons differ from one another by the nature of the receptor that they possess. However, the olfactory sensory neurons to which olfactory bulb neurons are connected are also distributed across the receptor sheet (the olfactory epithelium) depending on their chemical preferences. Locations on the olfactory epithelium and the olfactory bulb are correlated so, as with other sensory systems, the topographic map in the brain is linked to the structure of the peripheral organ. This principle is called rhinotopy.