What is a Dimension?

A dimension is a field holding qualitative information — names, categories, dates, geography. Tableau shows dimensions in blue in the Data pane.

Placing one on a shelf segments the view: it creates headers or splits marks into groups rather than producing a number. Dimensions answer *what are we looking at*, where measures answer *how much*.

Tableau assigns the role on connection based on data type, so text and dates become dimensions and numbers become measures. That guess is sometimes wrong — a Store ID is numeric but summing it is meaningless — and you fix it by right-clicking the field and choosing Convert to Dimension.

Worth separating from discrete versus continuous, which is a different question about how the field is drawn.