Guidelines for Preparing Effective Scientific Graphs

References:

Briscoe, Mary H., Preparing Scientific Illustrations, Springer-Verlag, New York, 204 pp., 1996

Definitions

Line - 2 bit black/white

Continuous or Halftone (8, 16 or 256 shades of gray)

dithering

random

pattern

Principles

Emphasize the data, not the axes or labels

Simplify axes

Avoid semilog axes if possible

Avoid “eye candy”

A good graph is uncluttered clear and focused

Symbols

Closed symbols more emphatic

Open and closed symbols have maximum contrast

Squares and circles look similar to each other

Size - depends on amount of data and precision

Size of symbols

Squares look larger than circles

Triangles look smaller than circles

Labels

Use compact spacing & labeling; Avoid wasted space

Short labels

Fonts - Use a Sans Serif font (e.g., Helvetica, Geneva, Arial)

Keep readable but minimize size to emphasize data

Upper and lower case, various sizes

Avoid bold labels, except for maximum emphasis

Legends

Keep simple

Avoid boxes

Titles

Upper case if short

Upper and lower case if longer

Axes

Linear vs semilog vs Log

Use Interior major and minor ticks

Minimize number of ticks

proportional to data resolution

readability

Use fewest significant digits

Eliminate unnecessary zeroes

Use compact x and y axes

Choice of origin

Use 0,0 if possible

If origin depends on data range, offset, separate, or break axis

Lines

Heavy lines connecting data

Thin error bars

If data equally important use solid lines only

Maximum contrast

solid (most important data)

dashed (2^nd)

dotted (least important)

Grids -

avoid - generally not useful

exception - if exact measurement is necessary

Boxes

Plot frames distracting, not necessary

Use of Color

Maps

Contours

Number

Line thickness

Use of Dashed lines

Labeling

San serif

Significant digits

Patterns

Acceptable patterns (ala Geology)

Grey half tones

at least 20% difference, 50% preferable

On reduction or reproduction

Diagonal hatching most pleasing and least ambiguous

Cross hatching darker and most emphatic (use fine lines)

Stippling becomes gray tone on reduction

Fine stippling drops out or becomes uneven

Images

Truth vs beauty

Use space wisely; avoid wasted space

Cropping size of picture for publication

Concentrate on features of interest

Tables

• Simple

• Clearly organized

• Logical groupings

• Self explanatory; complete

• Units defined

• Good use of space

• For slides - The simpler the better;

Only pertinent information

Types of Graphs

Pie - to compare percentages

Bar

Horizontal

Vertical

Stacked

Comparison of total measurements and subdivisions

Histogram

Frequency polygon

Line graph

for comparing equally spaced data on x axis (e.g., time)

Scattergraph

For examining relationships between 2 variables