How do we incorporate data and information (values and meanings) into a visualization that is clear, meaningful, and easy to understand? To achieve this goal, one of the basic information visualization design considerations is to effectively use visual elements and visual properties.
Visual elements are the basic building blocks in a chart or diagram to visualize data items. The most fundamental and abstract elements are: point, line, surface (area), and volume (3D). These basic elements, and the more complex elements built up on them, can represent almost anything in a visualization.
Visual properties are used to "decorate" visual elements, so that the values or meanings of data items can be directly and easily perceived and understood by human. I summarize the most commonly used properties as SSCOPe: Shape, Size, Color, Orientation, (spatial) Position, and Texture:
- Shape: shape can be applied to any visual elements. When used to visualize individual objects or data items, it usually represents nominal or categorical data values.
- Size: the size of an element is an important property used for continuous data values. It can be implemented as length, width, height, area, angle, etc. For various reasons, it is common that the size property does not directly and truly represent the underlying value. In these cases, it must be very careful to design the size property, because unreasonable distortions will impact human perception.
- Color: color is the most common visual property used for both categorical data and continuous data. It also include hue, brightness, and gray scale.
- Orientation: it is closely related to shapes, and can be seen as variations of a particular shape or pattern. An common example is arrows or hands pointing to different directions.
- Position: data values can be visualized as absolute positions in the visualization, or as the relative distance between elements. It is commonly used to visualize the position of data items against a pre-established scheme (such as a Cartesian coordinate system), categorization and grouping of date items in terms of similarities and differences, or spatial distances (especially used with maps).
- Texture: texture is important when color sensitivity is an issue. Implementations include fill patterns, border patterns, shadow, etc.
More complex visual elements (such as icons and symbols) can be built based on the basic elements and properties discussed above. Combinations of these properties can be used to represent multi-dimensional data in the same visualization. Animations (such as blinking, movement, spinning, etc.) are based on some dynamic changes of these properties, and they can be used for richer meaning and grab greater attention. Remember it is always a good idea to provide user customization of these properties.
