Annotations play a vital role in highlighting critical aspects of visualizations, aiding in data externalization and exploration, collaborative sensemaking, and visual storytelling. However, despite their widespread use, we identified a lack of a design space for common practices for annotations. In this paper, we evaluated over 1,800 static annotated charts to understand how people annotate visualizations in practice. Through qualitative coding of these diverse real-world annotated charts, we explored three primary aspects of annotation usage patterns: analytic purposes for chart annotations (e.g., present, identify, summarize, or compare data features), mechanisms for chart annotations (e.g., types and combinations of annotations used, frequency of different annotation types across chart types, etc.), and the data source used to generate the annotations. We then synthesized our findings into a design space of annotations, highlighting key design choices for chart annotations. We presented three case studies illustrating our design space as a practical framework for chart annotations to enhance the communication of visualization insights. All supplemental materials are available at {https://shorturl.at/bAGM1}.

翻译：标注在突显可视化关键方面、辅助数据外化与探索、协作意义建构以及视觉叙事中发挥着至关重要的作用。然而，尽管标注被广泛使用，我们发现当前缺乏一个针对标注常见实践的设计空间。本文评估了超过1800幅静态标注图表，以理解实践中人们如何对可视化进行标注。通过对这些多样化的真实世界标注图表进行定性编码，我们探讨了标注使用模式的三个主要方面：图表标注的分析目的（例如呈现、识别、总结或比较数据特征）、图表标注的实现机制（例如所用标注的类型与组合、不同标注类型在不同图表类型中的使用频率等），以及用于生成标注的数据来源。随后，我们将研究发现综合成一个标注设计空间，明确了图表标注的关键设计选择。我们通过三个案例研究展示了该设计空间作为图表标注实践框架的应用，以提升可视化洞察的传达效果。所有补充材料可通过 {https://shorturl.at/bAGM1} 获取。