Six rules to build a cohesive scientific figure

Use a consistent grouping criterion

First of all, if your scientific illustration has different elements, you want to group them so that viewers will be able to identify which elements are more related, and which ones are less related.

However, make sure you are grouping elements consistently throughout your scientific graphic or poster. Grouping different parts of the figure using a consistent criterion will help viewers make sense of what they are seeing. Choose a logical criterion and stick to it.

Use color to group elements of the same category

Color is a very powerful component in every image. It can serve many purposes in a scientific figure; undoubtedly, one of the most crucial of these is to guide the viewers to identify which elements are alike and which are not.

Let’s say you are presenting two different plots about the same set of variables. It is a good idea to associate each variable to the same color in both plots, so the readers can quickly understand what is going on. This helps viewers compare some elements across different parts of the figure.

If you want to make a distinction between elements that belong to two different groups, you can use color to set them apart. Using shades of one color for one group and shades of a different color for the other clearly signals to viewers that there is a distinction between the groups. You can achieve maximum contrast by choosing two complementary colors.

For example, the image above shows the secondary structure of a protein. In the right panel, alpha helices are colored in red and beta sheets in green. You can see for yourself that this panel is much more effective at communicating the secondary structure of this protein.

How to use color vs. greyscale

The contrast between greyscale and color can be effectively used to highlight a particular part of an image.

This is especially useful if you are presenting a picture or diagram of which you want to highlight a specific part. Maybe your picture is a bit complex and the viewer might be unsure where to look. If you have a black-and-white image with a colored part, the latter immediately catches the viewer’s eye, so that they can focus on the most important section.

You can also use the contrast between color and greyscale in plots or tables. Coloring specific data points, trend lines or table cells will clearly tell the readers that they should focus on those elements.

How not to use color

We have seen so far that color can be a very powerful tool for building a cohesive scientific graphic. However, you should also know when it is not a good idea to use it.

Color should not be used when it is not necessary to show relationships among elements on the page. If your figure only contains a couple different elements that belong in the same category, coloring them would just be a distraction. In this case, you are better off sticking to greyscale.

For example, if you are showing a list of amino acids that were present in your experiment, and all of them played a similar role, there is no reason to differentiate them by color. Take a look at the two images above: which one looks more clean and professional?

Group elements by proximity

One of the most straightforward, yet underrated ways to group elements in the figure is by proximity.

The principle here is simple: if elements are related, they should be near each other; if they are not, they should be far apart.

Blank space is a very underrated way to emphasize distinctions in scientific illustrations. As humans, we tend to avoid blank spaces because the void is scary. But if two or more groups of elements are different from each other, go ahead and leave more space between them! Your viewers will thank you.

Align items on your figure

Let’s add a final touch to make your scientific figure look more professional and organized: align all the items.

In general, there should be no element that is placed randomly on the page. Each element should have a spatial relation with some other elements in the figure.

For example, you can align the edges of plots, or the baselines of text pieces. This immediately gives the overall image a sense of feeling and organization, and creates a strong sense of unity.

Let’s recap!

There you have it! Six rules to build a cohesive scientific figure that will help your audience make sense of all the information. Let’s summarize them.

• Pick a logical criterion to group the elements of your graphic, and consistently stick to it.
• Use color to group elements of the same category.
• Use color vs. greyscale to highlight a part of the figure you want to bring attention to.
• Don’t use color when it doesn’t serve any specific purpose and would just be confusing.
• Group elements that are logically related to each other by placing them near each other; spatially separate elements that are not related to each other.
• Align the different items on your graphic to create a unitary and cohesive look.