Resolution

Option 1

Place a State field on Detail on the Marks card.

Option 2

1. Select Map > Edit Locations. 
2. In the Edit Locations dialogue box, do the following:

1. Display the Country/State/Province drop-down menu.
2. Select From field, and then select State.

Note: Where there are both ambiguous cities and countries in the view, you must edit the ambiguous countries before editing the ambiguous cities.

Cause

Some cities or counties have the same name but are located in different larger areas. As a result, Tableau Desktop does not know which of the multiple locations to plot.