In technical writing for clients, it’s often necessary to include numerical data in graphical or tabular form. Good tables and figures in technical writing make complex information much easier for the reader to digest. Generally speaking, engineers prefer graphs, which make it easy to see patterns and trends. Scientists, on the other hand, usually prefer tables of numbers. Choose what’s appropriate for the way your readers will want to use your report. Your client may also want the raw data in an appendix or an electronic spreadsheet for later use.
Tables and figures in technical writing (with their captions) should be understandable without reference to the body of the report. That is, the caption must provide enough of an explanation—including the definitions of any acronyms and abbreviations you may have used—to allow the reader to understand the table or figure by itself. Captions may be several lines long; there’s no need to limit them to a single line.
Much technical writing is based on data from other sources. Captions should credit the source(s) of anything you did not develop yourself. If you made the table or plotted the graph from someone else’s data, the credit should make that clear, for example, “Data obtained from Smith (2015).” If you’re reproducing the entire thing as is, just say, “Source: Jackson (2018).” If you’ve redrawn or reordered someone else’s work, say, “Adapted from Fong (2016).” If your source is a website, include the URL in the caption.
Figures include photographs, drawings, flow charts, and graphs. You may need to experiment to find the most effective way to convey the information visually. What works best for some readers may not be the best way for others, so consider who your readers are and how they will use this information.
Simpler is better. Try to eliminate extraneous details from your graphics so they’re clear and easy to read. In a written report you can have more detail than you’d want in an oral presentation, but extraneous details still detract from your message. For example, you may find that a drawing is better than a photograph to show how something works.
Make sure the image is large enough to show the details you want to depict. Lines must be bold enough to show clearly on the image at the size you’ve selected.
The caption goes below the figure. Make sure it stays on the same page as the figure.
In photographs, it’s important to give some indication of scale. This could be a person standing next to the object of interest, a ruler laid near the edge of the photograph, a person’s hand pointing to the feature of interest, or a common object such as a quarter placed next to it.
For a graph, clearly label the axes (including units). The axes should include 0; otherwise, the reader may get confused as to how significant the trend really is. Show the data points, not just the trend lines. If you show regression lines, you can label each line with its equation or include the equations in the caption. It may be better not to have a legend if that information can go into the caption.
Because some readers are colorblind, you should be judicious with color. Other readers will want to print out the figure on a black-and-white printer. Choose colors that will still be distinguishable in these situations. You can use dashed or dotted lines to help the reader distinguish them from solid lines.
The caption goes above the table. Make sure it stays on the same page as the table.
Choose a format that is clear and easy to read. Clearly label all row- and column headers. As with the figures, be judicious in your use of color. Usually, black lettering on a white background (without shading) is easiest to read.
If you do use color, it should mean something. For example, you could indicate acceptable alternatives with green and unacceptable alternatives with red.
Try to fit the whole table on one page. You can adjust column widths if necessary to make it work. You don’t have to use full sentences as your table entries; phrases will do. You can also use landscape format, and if 8-1/2 by 11-in. paper isn’t large enough you can use 11 by 17-in. paper. If you must break the table between pages, repeat at least an abbreviated version of the table caption and all the column headers at the top of each new page.
Number your figures and tables for easy reference. Make sure you call out every figure and table in the text of the report by number. Avoid using designations such as “above” and “below,” as you may have to revise the layout of your report so you don’t leave too much white space. It’s ok to put the figure or table before the text that refers to it. Just put them as close together as you can.
Start each section of your report with text rather than a figure or table. After the first paragraph, you can arrange your text, tables, and figures as needed to fill the page.
Well-thought-out tables and figures in technical writing can help you and your reader better understand even complex information in your report. Be aware that the way you select information to juxtapose in figures and tables has a tendency to highlight or obscure certain relationships–or suggest relationships where they don’t exist. That is, there are ethical implications to your selections of tables and figures.
You may find it easier to develop your figures and tables first. That will help clarify your thoughts, and you won’t have to write so much to get your ideas across.