The Visual Display of Quantitative Information
EDWARD R. TUFTE
Principles of Graphical Excellence
- Graphical excellence is the well-designed presentation of interesting data - a matter of substance, of statistics, and of design.
- It consists of complex ideas communicated with clarity, precision, and efficiency.
- Graphical excellence is that which gives to the viewer the greatest number of ideas in the shortest time with the least ink in the smallest space.
- It is nearly always multivariate.
- And it requires telling the truth about the data.
Principles of Graphical Integrity
- The representation of numbers, as physically measured on the surface of the graphic itself, should be directly proportional to the numerical quantities represented.
Lie Factor = (size of effect shown in graphic) / (size of effect in data)
- Clear, detailed, and thorough labeling should be used.
- Show data variation, not design variation.
- Graphics must not quote data out of context.
- The number of information-carrying (variable) dimensions depicted should not exceed the number of dimensions in the data.
Data-Ink
- This is the non-erasable core of a graphic, the non-redundant ink arranged in response to variation in the numbers represented.
Data-ink ratio = (data ink) / (total ink used to print the graphic)
Principles of data graphics
- Above all else show the data.
- Maximize the data-ink ratio.
- Erase non-data-ink.
- Erase redundant data-ink.
- Revise and edit.
Chartjunk
- This refers to over-busy grid lines and excess tricks, redundant representations of the simplest data, the debris of computer plotting, and many of the devices generating design variation.
- Forgo chartjunk, including moire vibration, the grid, and the duck.
Data-Ink Maximization
- When the principles of maximizing data-ink and erasing are applied to some graphical designs, e.g., the box plot and the scatter plot, new designs emerged.
- For the scatter plot, the frame lines can be edited to display the maximum, minimum, two quartiles, and the median for both variables.
Multifunctioning Graphical Elements
- A graphical element may carry data information and also perform a design function usually left to non-data-ink. Or it might show several different pieces of data. It is then called a multifunctioning graphical element.
- Principle is: Mobilize every graphical element, perhaps several times over, to show data.
- The graphical element that actually locates or plots the data is the data measure.
- Building data measures out of data increases the quantitative detail and dimensionality of a graphic, e.g., stem-and-leaf plot.
- Varying shades of gray show varying quantities better than color, they have a natural visual hierarchy.
- Different visual angles for different aspects of the data also organize graphical information. Each separate line of sight should remain unchanging (preferably horizontal or vertical) as the eye watches for data variation off the flat of the line of sight. For multivariate work, several clear lines can be created.
Data Density
- Data density = (number of entries in data matrix) / (area of data graphic)
- Principle is: Maximize data density and the size of the data matrix, within reason.
- As the volume of data increases, data measures must shrink.
- Graphics can be shrunk way down.
Small Multiples
Well-designed small multiples are:
- comparative
- multivariate
- shrunken, high-density graphics
- usually based on large data matrix
- drawn almost entirely with data ink
- efficient in interpretation
- often narrative in content, showing shifts in the relationship between variables as the index variable changes.
Aesthetics and Technique in Design
- Graphical elegance is often found in simplicity of design and complexity of data.
- Tables are the best way to show numerical values, although the entries can also be arranged in semi-graphical form.
- Tables also work well when the data presentation requires many localized comparisons.
The Friendly Data Graphic
- words are spelt out, elaborate encoding avoided
- words run from left to right
- little messages help explain data
- labels are placed on the graphic itself; no legend is required
- graphics attract viewer, provoke curiosity
- colors, if used, are chosen so that the color-deficient and color-blind can make sense of the graphic
- type is clear, precise, modest
- type is upper-and-lower case, with serifs
The Golden Rectangle
- If the nature of the data suggests the shape of the graphic, follow that suggestion. Otherwise, move toward horizontal graphics about 50 percent wider than tall.