This is fundamentally how Tableau works -- it will draw a mark for every intersection of dimension values (most of the time, the intersections must actually exist in the data). So adding a field as a dimension will potentially further slice the data and add new marks. The only exception is if you add a new dimension that doesn't add any new intersections of values.
So, for example, here you have 17 marks for every value of Category:
Adding the Department Dimension still results in 17 marks because each category only has one department.
But, adding a different dimension like Ship Mode instead, results in new intersections of values (though not all intersections exist in the data):
That's why adding dimensions causes your marks to be sliced -- it's because the dimension is doing it's job and further slicing the data.
Hopefully that helps explain why Tableau is behaving as you observe.
But... I'm thinking there might be some approaches to accomplishing your goals. Do you happen to have a packaged workbook or screenshot to share to help me better understand specifically what you want to accomplish?
Very nice explanation
Thanks for getting back to me. Here's the workbook with the issue in question with and a screenshot of the view with the formatting I want to see after adding the 'student number' dimension to the marks card. I need it in the view because I'm using it in an action filter for the dashboard. The problem is that I can't add it without it chopping up the marks by student and labeling each student as a percentage of the pane (as shown in the top image).
ClassSnapshotRevamp2.twbx 63.5 KB
Just curious... What happens if you add the StudentNumber pill to Tooltips instead of adding it directly to the data shelf?
I can't open your twbx to try it myself...
Yeah. I worried that might happen. I'm working in a cube, so that may have something to do with.
I tried adding the dimension to details and tooltips. It had no effect when added to details and I can't add it to the tooltp because it's a dimension, not a measure. I thought about converting it, but, and correct me if I'm wrong, I don't think action filters operate on measures.