Generally speaking everything we use in Tableau can be categorized as either a blue thing or a green thing. But what are these things and what makes them go blue or green?
For me the easiest way think about blue things is to imagine it as a feature that you can group data by. Whereas green things are what we are counting. For instance, if we were trying to understand which nation is the largest in the world we might want to group people by their nationality (a blue thing). Once we establish the different categories that we are interested in (e.g., British, American, Lithuanian) we need to find a way to determine the size of the nation. In this case we might want to count the number of people (green thing) in each country. So to reiterate it one more time, blue is something we can group things by while green is the thing that we are counting.
There are several other important differences between blue and green things that can help us set them apart:
1. Blue things are mostly dimensions. Green things are mostly measures. There are a few exceptions to this rule, the most notable being dates, but this is a guide for a beginner by a beginner so do not overthink it.
2. Blue things split up what is in the view. Green things fill up what is in the view.
3. Blue things create headers. Green things create axes.
4. Blue things are finite or discrete. Green things are infinite or continuous.
5. Blue things are always placed before the green things on the shelf. Not by choice, it is simply impossible to do it any other way.
