Consistency in design is important because it helps the readers understanding and interpretation of the data they are looking at. This in turn helps save time and energy, because the reader of the information doesn’t have to learn new ways of looking at data that is similar.
There are several ways in which consistency can be established:
1. Using identical formatting for elements that cary the same meaning. This can be presented with labels that are the same size, typefaces, weight, and color. Visualization of similar data should use the same flavor of representation, but also in the context of what type of data is represented. For example using the same representation method in the summary location of a dashboard and the area for more specific and detailed information (see http://blog.bettinakast.me/how-to-organize-dashboards-for-the-best-results/ ) in contrary can slow down the user, as they are missing an anchor their eyes can hook onto.
2. Color is often used by readers as a means to identify categories. Using the same color across various locations on a dashboard will also very likely lead readers to interpret the data as of the same type. Color should hence be used in such a way that it is associated with one and the same meaning across all dashboard locations.
Inconsistent dashboard design leads to lost time and energy, frustration and annoyance, as the reader is forced to constantly re-evaluate and interpret the data.