The number of categories depends mainly on what you want to show:
- To show general trends, the number of categories can be larger (up to 50 columns);
- To show comparisons between categories, it is better to reduce the number of categories (up to 12 categories).
On the 'Visually' page we can read that in any case, when making comparisons, we need to go below 12 categories, and preferably to as few as possible. When displaying trends, we can go up to 50 columns if this gives a more illustrative view of the trend.
Additionally, the 'Visually’ website suggests that we should set the limit under 12 categories when we are comparing within categories - the lower the number of categories, the better.