Visualizing dynamic data is an aesthetic and readability challenge in dashboard design. In most cases, the amount of data will change depending on how the user interacts with the dashboard.
One example is the filtering of a trend chart (Figure 1). The following image shows a line chart from Jan. 2010 to Dec. 2010. In addition, there’s a filter that allows the user to select the range of time to see.
Figure 1 - A trend chart
Now, for whatever reason, the user decides to select Jan. 2010 to Feb. 2010. The chart looks like this.
Figure 2 - A trend chart that looks visually awkward
The data will not be misinterpreted but it does look unprofessional. The solution I prefer to use is having a minimum range that must be selected for the end user. In this particular example, the size of the visualization allows for at least 12 months of data to be displayed. Therefore, in the date range selection, I would not allow the user to choose an end date that shows less than 12 months worth of data. For example, if the user chose Jan. 2010 as the start date and Mar. 2010 for the end date, the dashboard would simply change the end date to Jan. 2010. This ensures the chart will always look proper.
Another example is a dashboard that contains a visualization that compares the values of a list. For example, you have a bar chart that compares how sales reps are doing against each other. In addition, there is a filter that allows you to choose which reps to show.
Figure 3 - Clear comparison chart
Now, if you wanted to compare more reps, this will eventually happen (depending on the number of reps you have).
Figure 4 - An unreadable bar chart
This is a serious visualization issue. You can’t read the names of the reps. However, this can be avoided by just choosing the right visualization. The first step is trying to understand the purpose of the dashboard and the metric. In most cases, this visualization is used to compare a list of values. The dashboard designer has to ask the end user, “Do you need to see so many reps at once?” In my experience, that has been 'no' all the time. In fact, people usually want to see the top N or bottom N in the list. This will help choose the right size for the visualization. If the end user really wants to see a specific item in a list, there should be a control to help with this. For example, the top 10 reps would be shown, and the end user can select a particular rep to add to the list. The point is, the dashboard should limit the end user from adding more than what can be seen in the visualization.