Any two dimensional set of numbers, colors, intensities, sized dots, or other glyphs.
Nominal, ordinal and interval-ratio types are all good fits for this visualization.
They are used to give a quick overview of the distribution and proportions of each sample in a data set and also to compare distribution and proportion across other datasets, in order to discover patterns.
i.e. When two items are being compared against one another in a the D' table.
Given the richness and potential variegation of the data in each cell (Ex: a number within a variable sized and colored circle) a mapping methodology needs to be determined which is intuitively understandable and expresses the importance of each cell attribute relative to all others. Ex: An income range might be better suited to a color or size intensity rather than a glyph. If a zip code is a relevant but less important attribute of a cell, it should not be mapped in a way where it is the first thing noticed.
- Completely different colors can be used for nominal samples.
- Intensities of colors can be used to express ranges of ordinal or interval-ratio samples.
- Completely different sizes can be used for nominal samples. (Not recommended for datasets with many potential nominal values)
- Variations in size can be used to express ranges of ordinal or interval-ratio samples.
- Best suited to nominal samples.
- Can be used for ordinal but not recommended for datasets with many potential ordinal values.
This is a special case of a square matrix wherein the samples above the main diagonal are reflections of those below or are zero.
Mapping choice could allow one cell to obscure or overlap another.
Redundant data shown. A half matrix might have been better suited.
Group designations on axes are unnecessarily opaque.