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.

中文翻译：

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探索背景图像透明度对图像地图可用性的影响

影像地图是影像与地图之间的折衷，是利用影像的真实感和地图固有的高解释效率的有效手段。由于以卫星图像为背景，此类地图的制图设计与传统制图有很大不同。为了使此类地图更有效，已经进行了一些研究，以通过调整背景图像的透明度、对比度和饱和度来降低背景图像的复杂性。然而，这种探索并没有系统地进行。本研究侧重于背景图像的透明度对图像地图的可用性（即有效性和效率）的影响。用户研究通过在线问卷调查进行了广泛的实验。实验数据集包括具有 11 级图像透明度、三个尺度和九个区域的图像地图。1,263 名参与者参加了这项实验，他们被要求区分自然和文化特征。已经发现： (a) 图像地图的可用性随背景图像的透明度而变化，多为单峰；(b) 与峰值可用性相对应的透明度级别随着背景复杂性的增加而降低。这为在图像映射设计中有效使用透明度提供了指导。多为单峰；(b) 与峰值可用性相对应的透明度级别随着背景复杂性的增加而降低。这为在图像映射设计中有效使用透明度提供了指导。多为单峰；(b) 与峰值可用性相对应的透明度级别随着背景复杂性的增加而降低。这为在图像映射设计中有效使用透明度提供了指导。