Designing Charts: Using Zero Baselines

A zero baseline is the point where the axis of a chart starts at zero, making it easy to compare values and assess differences more accurately. It is essential to use a zero baseline in charts, like bar and column charts, where the length or height of the bars represents a value directly. 

Determining when to use a zero baseline:

  • Display data accurately: If the goal of your visualization is to give an honest and precise representation of your data, a zero baseline is crucial. For example, when showing sales figures, using a zero baseline helps the audience easily understand the sales difference between two time periods.  
  • Easy comparisons: Using a zero baseline can simplify comparisons if you are comparing different data items. For instance, when comparing the population of multiple countries on a bar chart, a zero baseline will easily show which country has the highest or lowest population.

When to NOT use a zero baseline:

  • Focus on small differences or trends: When visualizing data where the focus is on understanding small differences or trends, a zero baseline might not be helpful. In that case, a line or area chart can be used instead. For instance, if you want to show the fluctuation of stock prices within a short period, a line chart without a zero baseline will help focus more on the trend.
  • Logarithmic scale: When visualizing data that span multiple orders of magnitude, a logarithmic scale could be more appropriate, and a zero baseline may not be used. For example, a chart showing earthquake magnitudes or the growth of social media users over the years would benefit from a logarithmic scale.

In conclusion, determining when to use a zero baseline depends on the type of data you are visualizing and the goals of your chart. In general, when displaying data that requires accurate and easy comparisons, a zero baseline is beneficial, but when focusing on small differences or trends within the data, other visualization methods might be more suitable.