Presenting time-related categorical data can be tricky. Fortunately, there are some good practices which guide us on how to approach the topic. In this article, you can find a summary of DOs and DON’Ts upon a subject.
The first well-documented calendar systems, which portray the linear nature of the time, appeared in the archaeological record around 5’000 BC. Most of us feel the pressure of time. To express it, we use common sayings like “Time is money” or “Time waits for no one”.
The culture shaped human time perception. We think about the time as the arrow shot into space. That has, of course, the impact on data visualization aspect. There are three basic rules regarding presenting data in the context of time. By following them, people easily digest information and form conclusions.
1. Use left-right direction.
2. Keep chronological order.
3. Use typical time units.
Another thing to consider is proper visualization. The decision of using one visualization than another depends on the aspect of continues or categorical data type. Continuous data have only one option — line graph. However, categorical data, which are clustered in periods or bins, can be more tricky.
In today’s scenario, let’s imagine that we present outcomes (level of satisfaction) from the survey grouped by respondents age. What would be the best choice when the data dimension is embedded in time, but not expressed in typical time units?
Stacked bar chart
The general rule is to present categorical data on a stacked bar chart (using Y-axis), with proper descending sorting. Nevertheless, categories which are linked with the time, for instance: age bins, archaeological periods, process’s phases, the human brain decodes much easier on X-axis, starting from left and ending on right.
Stacked column chart
Presenting time-related categories on X-axis is good to remember to keep chronological order. Like in this example, sorting descending categories by the value are not very effective. The audience must use a cognitive power to understand the meaning of X-axis and figure out the order of age bins in the survey population.
Stacked column chart (chronological order)
Then, when we placed categories on X-axis with chronological order, and like in this example the order is from younger to older, we tell the story of distribution of survey outcomes among respondents population in the age group context. Combination of a column chart and X-axis embeds us within the context of population distribution and helps remember the results.