A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Keep the image as simple as its content allows
Presenting evidence in tables and figures
Part I. Research and writing: from planning to production

Some guides encourage you to put as much data as you can in every graphic, but readers want to see only the data relevant to your point, presented in an image free of distractions:

1. Include only relevant data. If you want to include data just for the record, label it accordingly and put it in an appendix (see A.2.3).

2. Make the grid simple.

Graphics

Box a graphic only if you group two or more figures.

Do not color or shade the background.

Never create a three-dimensional background for a two-dimensional graphic. The added depth contributes nothing and can distort how readers judge values.

Plot data on three dimensions only when you cannot display the data in any other way and your readers are familiar with such graphs.

Tables

Never use both horizontal and vertical lines to divide columns and rows. Use light gray lines if you want to direct your reader's eyes in one direction to compare data or if the table is unusually complex. Avoid using gray lines or shading in anything that will be microfilmed, because the photographed image may be blurred.

For tables with many rows, lightly shade every fifth row.

Do not use a font size smaller than nine points for a document that will be microfilmed. Smaller fonts will be illegible.

Charts and Graphs

Use grid lines only if the graphic is complex or readers need to see precise numbers. Make all grid lines light gray, unless the text will be microfilmed.

Color or shade lines or bars only to show a contrast. Use color only if the text will be printed in color and not photocopied later. (Black-and-white photocopies make many colors look alike.)

Never create a three-dimensional chart or graph if you can represent the same data in two dimensions. The added depth contributes nothing and can distort how readers judge values.

Never use iconic bars (for example, images of cars to represent automobile production). They add nothing, can distort how readers judge values, and look amateurish.

3. Use clear labels.

Label rows and columns in tables and both axes in charts and graphs. (See chapter 26 for the punctuation and spelling of labels.)

Use tick marks and labels to indicate intervals on the vertical axis of a graph (see fig. 8.4).

If possible, label lines, bar segments, and the like on the image rather than in a caption set to the side. Use a caption only if labels make the image too complex to read.

When specific numbers matter, add them to bars, segments, or dots on lines.