Annotations are a vital component of data externalization and collaborative analysis, directing readers' attention to important visual elements. Therefore, it is crucial to understand their design space for effectively annotating visualizations. However, despite their widespread use in visualization, we have identified a lack of a design space for common practices for annotations. In this paper, we present two studies that explore how people annotate visualizations to support effective communication. In the first study, we evaluate how visualization students annotate bar charts when answering high-level questions about the data. Qualitative coding of the resulting annotations generates a taxonomy comprising enclosure, connector, text, mark, and color, revealing how people leverage different visual elements to communicate critical information. We then extend our taxonomy by performing thematic coding on a diverse range of real-world annotated charts, adding trend and geometric annotations to the taxonomy. We then combine the results of these studies into a design space of annotations that focuses on the key elements driving the design choices available when annotating a chart, providing a reference guide for using annotations to communicate insights from visualizations.

翻译：标注是数据外部化和协作分析的重要组成部分，能够引导读者关注关键视觉元素。因此，理解其设计空间对于有效标注可视化至关重要。然而，尽管标注在可视化中被广泛使用，我们发现针对标注常见实践的设计空间仍存在空白。本文通过两项研究探索人们如何标注可视化以支持有效沟通。第一项研究中，我们评估了可视化专业学生在回答关于数据的高层次问题时如何标注柱状图。对标注结果进行定性编码后，生成包含封闭图形、连接线、文字、标记和颜色的分类体系，揭示了人们如何利用不同视觉元素传递关键信息。随后，通过对多样化真实世界已标注图表进行主题编码，我们扩展了该分类体系，新增趋势标注和几何标注。最后，我们将两项研究结果整合为一个聚焦标注图表时驱动设计选择关键要素的标注设计空间，为使用标注传递可视化洞见提供参考指南。