This dissertation focuses on viewers' perception of the relative size of words presented in tag clouds. A tag cloud is a representation of the word content of a source document where the relative frequency, or importance, of the keywords (i.e., tags) is depicted by presenting the most important tag words in a cluster called a tag cloud and varying visual characteristics of the tag words such as color, saturation, location and size. Although previous research has found that relative size is a strong visual factor for communicating relative importance of tag words, it is still unclear how viewers perceive the relative size of the words in tag clouds and how perceived size is influenced by other tag cloud characteristics. This dissertation looks at how viewers estimate the relative size of words given different characteristics such as decorations like (e.g., filled areas, boxes, and shadows), appearance of the words (e.g., varying the amount of narrow or wide letters), the typeface style (e.g., bold typeface), and location in the tag cloud (e.g., upper left vs. upper right quadrants). Significant under- and over-perception of the relative size of tag words were observed, primarily varying with the size of the target tag word. Word appearance had a modest effect on size misperception, while typeface style and location had a smaller effect. The results provide insight regarding the influence of surrounding tags on the perception of relative size of a tag word, as well as guidance to tag cloud designers regarding the influence of other presentation characteristics on perceived relative size
