The shape mark type is useful when you want to clearly see individual data points while also viewing categories associated with those points. Tableau displays your data using a shape when:
The Mark menu is set to Automatic,
and you place one or more measures on both the Rows and
the Columns shelves.
You select Shape from the Marks menu.
By default, the shape used is an open circle. You can select a different shape by clicking Shape on the Marks card. Twenty unique shapes are available:
To add more data to the view, you can place a field on Shape. Tableau separates the marks according to the values in the field. If the field is a dimension, each member is assigned a unique shape. If the field is a measure, the measure is automatically binned into distinct buckets and each bucket is assigned a unique shape. The shape legend displays how shapes are distributed.
As shown below, the Ship Mode dimension is used on Shape to encode each mark with information about how the order was shipped.