Day 1 — What Tableau is, and dimensions vs measures

One idea does most of the work in Tableau. Get it and the rest follows quickly.

Tableau asks two questions of every field

When Tableau connects to your data it sorts every column into one of two buckets, and almost everything else follows from that choice.

Dimension	Measure
Something you slice by	Something you add up
Region, Category, Order Date	Sales, Quantity, Profit
Usually text or dates	Always numbers
Shown in blue	Shown in green
Creates rows in the view	Gets aggregated inside them

The test that always works Would you ever want to see this field totalled? Then it is a measure. Would you want to group by it? Then it is a dimension. A postcode is numeric but nobody sums postcodes - it is a dimension.

The data source

Every calculation on this page runs against the Orders data source below - 48 rows, dimensions in blue, measures in green, exactly as Tableau colours them.

Blue headings are dimensions, green are measures. Order ID is a number but it is a dimension - you would never add order numbers together.

Your first calculation

A calculated field is a new column you define with a formula. This is the whole language you will learn over the next eleven days.

Edit it and press Run. Try SUM([Profit]) or COUNT([Sales]).

Dimensions build the view

Drop a dimension on Rows and Tableau splits the numbers by it. You wrote one calculation; the view supplies a different set of rows to each line.

Change data-by in your head to Category, Manager or Ship Mode - the same calculation answers a different question each time. That is the point of Tableau.

What this tutorial can and cannot do

Tableau Desktop is an application you drag things around in. A web page cannot be that. But the calculation language is a language, so that is what this tutorial teaches and runs - real calculated fields, evaluated against a real data source, including level-of-detail expressions.

Not covered here Dragging pills onto shelves, choosing mark types, dual axes, dashboard layout, Tableau Server and Tableau Public. Those need the application in front of you - that is the classroom course. What you will get here is the part people actually get stuck on: why a number is wrong, and how to write the calculation that fixes it.

Try these yourself

Decide whether Ship Mode is a dimension or a measure, and say why.
Write a calculation for total quantity sold.
Count how many distinct products appear in the data.
Break Total Sales down by Manager instead of Region.
Explain why Order ID is a dimension even though it contains numbers.

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