AnnoGram: An Annotative Grammar of Graphics Extension

TL;DR

This paper introduces AnnoGram, a declarative extension to the Grammar of Graphics that treats annotations as first-class elements, improving expressiveness and reusability in data visualization.

Contribution

It presents a novel annotation extension to Wilkinson's Grammar of Graphics, enabling structured, reusable, and portable annotations within visualization workflows.

Findings

Enhanced expressiveness in visualization annotations

Reduced authoring effort compared to existing tools

Enabled portable and semantically integrated annotation workflows

Abstract

Annotations are central to effective data communication, yet most visualization tools treat them as secondary constructs -- manually defined, difficult to reuse, and loosely coupled to the underlying visualization grammar. We propose a declarative extension to Wilkinson's Grammar of Graphics that reifies annotations as first-class design elements, enabling structured specification of annotation targets, types, and positioning strategies. To demonstrate the utility of our approach, we develop a prototype extension called Vega-Lite Annotation. Through comparison with eight existing tools, we show that our approach enhances expressiveness, reduces authoring effort, and enables portable, semantically integrated annotation workflows.