The square mark type is useful when you want to clearly see individual data points. When you select Square from the Mark menu, Tableau displays your data using squares.
The data view shown below displays several dimensions in both the rows and columns of a table. If the Mark menu was set to Automatic, the data would be displayed using text. By manually selecting Square, you create a completely different view. In particular, by placing a measure on Color, you can use square marks to create a heat map. To try some hands-on exercises for building heat maps, see Building Heat Maps.
To reproduce this view, you may need to select Cell Size > Square Cell from the Format menu on the toolbar, and then adjust the size of the squares using the Size slider.When you add additional levels of detail by placing a dimension on the Detail, Color, Shape, Size, or Text target on the Marks card, the squares are shown side-by-side and wrap to fill the cell. If the application window is too small to show all of the squares, an ellipses is shown to indicate that there are more values than can be shown.
You can also use the square mark to create treemaps. A treemap displays hierarchical data as a set of nested rectangles. To try a hands-on exercise for building a treemap, see Building Treemaps.