What is Aggregation & Disaggregation?

Aggregation is combining many rows into one value — summing, averaging, counting. Tableau aggregates measures automatically, because each mark in a view can only display a single number.

You can see the aggregation in the pill itself: `SUM(Sales)` rather than `Sales`. Change it from the field's dropdown, or set a different default in the Data pane.

Disaggregation turns that off. Analysis → uncheck Aggregate Measures, and Tableau plots one mark per underlying row instead of one per combination of dimensions.

Disaggregating is useful for spotting distribution and outliers — a scatter plot of every transaction rather than a single summed point. On a large data source it produces a great many marks, so it is an exploration tool rather than something to leave on in a dashboard.