Visual encoding
From WikiViz
The visual encoding is the way in which data is mapped into visual structures, upon which we build the images on a screen. It is defined in term of:
- Spatial substrate
- Graphical marks
- Graphical properties of the marks
Spatial substrate
The spatial substrate define a position of the space where we collocate graphical marks. The space is defined in term of axes. Card et al. (1999) define four elementary types of exes:
- Unstructured axis (no axis)
- Nominal axis (a region is divided into sub regions)
- Ordinal axis (the order of the axis correspond to the order of the data)
- Quantitative axis (there is a metric associated with the region)
In order to increase the quantity of data that can be encoded with in a single representation, Card et al. (1999) identified some techniques:
- Composition
- Alignment
- Folding
- Recursion
- Overloading
Graphical marks
Marks are graphical entities visible to the humans located somewhere in the space. According to Bertin (1983) and Card et al. (1999) there are four elementary types:
- Points
- Lines
- Areas
- Volumes
Graphical properties for marks
Graphical proprieties (also called retinal proprieties) are proprieties processed by retina of the eyes which is sensitive to them independent of position. Bertin (1983) identify 6 retinal proprieties:
- Colour
- Size
- Orientation
- Gray Scale
- Texture
- Shape
Card at al. (1999) also add two proprieties which are considered in Information Visualisation:
- Connection
- Enclosure
