ABSTRACT
Marks are basic geometric elements that depict items or links, and channels control their appearance. The effectiveness of a channel for encoding data depends on its type: the channels that perceptually convey magnitude information are a good match for ordered data, and those that convey identity information with categorical data. Learning to reason about marks and channels gives the building blocks for analyzing visual encodings. The core of the design space of visual encodings can be described as an orthogonal combination of two aspects: graphical elements called marks, and visual channels to control their appearance. Even complex visual encodings can be broken down into components that can be analyzed in terms of their marks and channel structure. A visual channel is a way to control the appearance of marks, independent of the dimensionality of the geometric primitive. A few of the many visual channels can encode information as properties of a mark.
