Protovis: A Graphical Toolkit for Visualization
Despite myriad tools for visualizing data, there remains a gap between the notational efﬁciency of high-level visualization systems and the expressiveness and accessibility of low-level graphical systems. Powerful visualization systems may be inﬂexible or impose abstractions foreign to visual thinking, while graphical systems such as rendering APIs and vector-based drawing programs are tedious for complex work. We argue that an easy-to-use graphical system tailored for visualization is needed. In response, we contribute Protovis, an extensible toolkit for constructing visualizations by composing simple graphical primitives. In Protovis, designers specify visualizations as a hierarchy of marks with visual properties deﬁned as functions of data. This representation achieves a level of expressiveness comparable to low-level graphics systems, while improving efﬁciency--the effort required to specify a visualization--and accessibility--the effort required to learn and modify the representation. We substantiate this claim through a diverse collection of examples and comparative analysis with popular visualization tools.