Tips for Text Positioning on Data Visualizations
You may have heard the saying "It's all about where you place it," which could not be truer when it comes to adding text to data visualizations. Wrongly placed text can lead to misinterpretation of the data.
You should follow two best practices in placing text on your data visualizations:
Keep all text horizontal. Nonhorizontal text may confuse some of your potential users. It's strongly advised that you stay away from positioning your text vertically or diagonally. Never force a user to tilt his/her head to read something! Stick to the basics by keeping all text horizontal.
Keep in mind that text is included to complement the visual, not overshadow or complicate it.
Keep all text within range of the visual. The human eye naturally associates any text within a few centimeters of it as being related to it. In general, ensure that all text is within the range of the visual it's related to, because positioning text too far from the targeted visual can lead to confusion.
The following figure shows two basic bar charts. Both charts have a title label, which is one of the most intuitive and common uses of text in any data visualization. The chart on the left has an easy-to-read horizontal label; the chart on the right has the same label tilted. Do you have to tilt your head to read the chart on the right? That label might be mistaken for an axis label.