Exploring the effects of background image transparency on the usability of image maps

Abstract

Image maps, a compromise between images and maps, are an effective means of harnessing the advantages of realism from images and the high efficiency of interpretation inherent to maps. As satellite images are used as the background, the cartographic design of such maps is quite different from traditional mapping. To make such maps more effective, some investigations have been conducted to reduce the complexity of background images by adjusting their transparency, contrast, and saturation. However, such exploration is not systematically carried out. This study focuses on the influence of the transparency of background image on the usability (i.e., effectiveness and efficiency) of image maps. Extensive experiments were conducted by user studies via an online questionnaire survey. Experimental datasets included image maps with 11 levels of image transparency, at three scales and in nine areas. 1,263 participants took part in this experiment, in which they were asked to distinguish natural and cultural features. It has been found that: (a) the usability of image maps varies with the transparency of background image, mostly with a single peak; and (b) the transparency level corresponding to the peak usability decreases with an increase in background complexity. This provides a guideline for effective use of transparency in image‐map design.