Object Size Discrimination and Non-visual Cartographic Symbolization

Guidelines for cartographic symbolization, developed over several hundred years, have focused almost exclusively on visual design elements for maps. Recent attention on the personal computer and the Internet as a means for map display and map dissemination has resulted in more discussion about symbolization guidelines, particularly in settings where the scale of map display is dynamic and where extra information is added to maps with auditory and haptic interface devices. The additional information presented in the auditory and haptic sensory domains is usually intended as an augmentation for a standard visual map. Maps produced for the blind and visually impaired, in contrast, are not designed with visual symbolization as a primary concern, but are intended for communicating geographic information without reliance on visual interaction. In this non-visual map design setting, rules for cartographic symbolization are needed that are not simply extensions of visual design guidelines, but are rather derived from human subjects testing and existing theories from the perceptual and cognitive sciences. In this paper, we present some evidence from human subjects testing that suggests size discrimination guidelines for cartographic symbols presented in the auditory and haptic sensory domains, with a goal of adding to the body of work on map design for blind and visually-impaired individuals.