Just like a road atlas faithfully maps real-word locations, our brain maps many aspects of our physical world: Sensory inputs from our fingers are mapped next to each other in the somatosensory cortex; the auditory system is organized by sound frequency. The olfactory system was believed to map similarly, where groups of chemically related odorants – amines, ketones, or esters, for example – register with clusters of cells that are laid out next to each other.