The Design of Tactile Thematic Symbols

The study reported here investigated the design and legibility of tactile thematic maps, focusing on symbolization and the comprehension of spatial patterns on the maps. The results indicate that discriminable and effective tactile thematic maps can be produced using classed data with a microcapsule paper production method. The participants demonstrated that they could describe the spatial data patterns that were displayed. ********** Thematic maps are cartographic representations of themes, such as population or income. These types of maps can show information about specific locations, give general information about spatial patterns, and be used to compare the patterns on two or more maps (Slocum, McMaster, Kessler, & Howard, 2005). The importance of this cartographic method is evident in the sheer volume of scholarly papers and books on thematic mapping that provide guidelines that inform both the theoretical and design components of making these types of maps for sighted map users. Research has focused on creating tactile map symbols and formalizing the techniques in tactile mapping, including the articulation of good practices (Tatham, 2003). However, the development and use of symbols for static tactile thematic maps has not been studied extensively. The lack of attention is not due to the absence of need, however; researchers and practitioners have expressed a clear need for the development of effective tactile thematic maps (Lobben, 2005). Even though thematic mapping has been a popular cartographic method for nearly 200 years, we cannot directly apply knowledge of the design of symbols for printed thematic maps as a guide for the creation of tactile symbols, given that it is often inappropriate to translate print map symbols into a tactile map format (James, 1982; Klatzky & Lederman, 1987). But, as we discuss later, several principles of cartographic design may be shared between the thematic design of tactile and visual symbols, such as max-contrast symbolization (Cromley, 2005; Dougenik & Sheehan, 1975; Gilmartin & Shelton, 1989), half-toning (Slocum, 1999), and nonlinear assumption (Kimerling, 1985). In the study presented here, we borrowed and applied these guidelines for making traditional print thematic maps to the design and subsequent evaluation of tactile thematic maps. A primary goal of the research was to identify effective symbols for tactile thematic maps. An effective symbology is based on discriminability and the extent to which the symbols foster spatial understanding. The two research questions that drove the experimental design and data analysis were these: 1. Can the tactile map user discriminate among the different fill patterns that are used to represent distinct classes of maps? 2. Can these symbols be used to create a classed quantitative choropleth tactile map that facilitates the recognition and overall understanding of spatial patterns, such as the population distribution of a state? Symbolization and use of tactile maps A critical area of research in tactile mapping involves the legibility and meaningfulness of tactile symbologies (Lambert & Lederman, 1989). The reading of tactile maps consists of a series of processes, beginning with the discrimination and identification of symbols (Perkins, 2002). Early studies of legibility included those on the effect of noise in detecting point symbols (Berla & Murr, 1975); minimum sizes for areal and point tactile symbols (Nolan & Morris, 1971); and the identification of one symbol among a series of symbols of the same class, either points, lines, or area (Barth, 1982). Barth, along with others (Gill & James, 1973; Lambert & Lederman, 1989), used a matching task or a paired comparison task in which a single symbol was identified among a set. These studies are relevant because they mimicked behavior that would be performed with a map legend. …