Goal: Communicate information
Author (you) -> graphic -> Reader
A graph is more effective than another if its quantitative information can be decoded more quickly or more easily by most observers.
Nancy Robbins, Creating More Effective Graphs
Detection: recognition of geometry encoding values
Assembly: grouping of detected symbol elements
Estimation: assessment of relative magnitude of values
Position along a common scale (most accurate task)
Position along identical nonaligned scales
Angle and slope
Color: hue (red, green, blue, etc.), saturation (pale/deep), and lightness. Hue can give good discrimination but poor ordering.
Show the data
Avoid distorting the data
Label data, minimize legends
Use clearly different symbols, colours
Dot plots are often better than bar charts