If I understand you correctly, you wish to view the map as Country sometimes and as City at other times. Given the cities and countries you listed, I was able to create it without any problems (assuming you use a workbook to view it). When I click on the plus beside Country to look at City level detail, the map updates properly (see attached).
However, when using a dashboard, there is no way to click on the '+' as it is within the level of detail. Using a parameter to switch between the two does not work either. If this is what you're doing, you would need two maps (one for city and one for country). A parameter could then be used to toggle between the two maps so only one is displaying at a time. http://kb.tableausoftware.com/articles/knowledgebase/creating-sheet-selector-for-dashboard may be of help along these lines.
Hope this helps,
test.twbx.zip 85.1 KB
Looks like using a parameter is my only option then. I will try this. Thanks for your help.