Polygon Mark

Polygons are points connected by lines enclosing an area. The polygon mark type is useful when you want to connect points to create data areas. Tableau displays data using polygons when you select Polygon from the Mark menu.

The polygon mark is not commonly used and often requires a specially constructed data source.

The view shown below comes from a specially constructed data source that holds geographic and election data. It displays the 48 contiguous US states as a function of latitude and longitude and color-encodes each state by the 2000 presidential election results.
If Mark is set to Automatic, the data will be displayed using a shape. Manually selecting Polygon and adding additional fields to the view causes a different view to be created.

Every state is considered to be a polygon in the data source. The PolygonID field on the Detail target is distinct for each US state. You can remove states from the view by filtering this field.
Additionally, you can specify the drawing order of the lines that constitute each polygon by placing a field on the Path target. In this example, the PointOrder measure is used to draw each state.