Large sections of the brain in most mammals are devoted to processing sensory information from the outside world.  These range from the primary visual area to the auditory cortex to the somatosensory region.  Each of these regions is organized in a way that presents a "map" of the world.  For example, the primary visual cortex is organized so that one large strip of cells are activated by stimulation close to the center of visual focus.  An adjoining strip of cells is activated by stimulation very slightly off-center, and each adjoining strip represents a circular area slightly farther from the center of focus. Actually, the previous description is only an approximation.  In actuality, such brain regions integrate stimuli from various sources which have to share the "surface" of cells available on the input layer.  For example, left and right eye inputs both arrive on the same layer, and though the overall "map" is the same for both eyes, the individual cells are not randomly intermixed.  Instead, they are highly organized into stripes ("ocular dominance columns") with each stripe containing cells activated only by one eye.  Yet the representation still maps the real world.  Imagine printing the left-eye image onto a rubber sheet that is stretched, then cutting random slits in it:  the image remains, but now has gaps.  In these gaps lie the shrunken representation from the right-eye image. We call these regions  "polymaps" as they represent the intermixed mapping of several world representations onto a single surface.