Differences in appearance always prompt us to search, whether consciously or unconsciously, for the significance of those differences. Anything that means the same thing or functions in the same way ought to look the same wherever it appears on a dashboard. Even something as subtle as arbitrarily using dark axis lines on one graph and light axis lines on another will lead viewers to suspect that this difference, which is in fact arbitrary, is significant.
It's important to maintain consistency not only in the visual appearance of the display media, but in your choice of display media as well. If two sections of data involve the same type of quantitative relationship (such as a time series) and are intended for similar use (for example, to compare a measure to a target measure for each month), you should use the same type of display for both (for example, a bar graph). Never vary the means of display for the sake of variety. Always select the medium that best communicates the data and its message, even if that means that your dashboard consists of the same type of graph throughout.
Clarifying the Vision
Variations in Dashboard Uses and Data
Thirteen Common Mistakes in Dashboard Design
Tapping into the Power of Visual Perception
Eloquence Through Simplicity
Effective Dashboard Display Media
Designing Dashboards for Usability
Putting It All Together