Examining the characteristics of a graphical map display relative to cognitive structure can nevertheless be illuminating with regard to the characteristics of the mental representation of geographic space. Most of our geographic knowledge, is not actually stored in any sort of graphic form, cartographic or otherwise. They are perhaps best described as image representations that have been possibly, but not necessarily, derived from some visual stimulus. Most adults are familiar with imagery conjured-up from reading a novel or a poem, or by listening to music. Just on the basis of intuition, perhaps with a little introspection, this doesn't ring true.
External representation can take many forms, including words, images, diagrams and maps.
We must therefore maintain a careful and conscious distinction between external and internal forms. All of these can be recalled as sensory sensations, whether they are completely imagined or based upon actual sensory experience. From the Piagetian perspective, sensory sensation is the beginning of learning. This consists of what might be termed experiential or observational knowledge - i.e., stored sensory sensation and is not abstract or derived knowledge. On this basis it would seem reasonable to say that such knowledge could be cognitively encoded as stored sensory sensations - which indeed could include a visual recollection of words on a printed page.