Area contains countries contains cities....
I'd be inclined to have the user select the Area, then the country, then the city--stopping when there is nothing further to specify. Each selection can be part of a hierarchical conditional value list where each choice filters the avialable values in the next field's value list.
Example: Select Med in the area field and the list of countries filters down to just countries from the Mediterranian area. Select Spain and the list of cities narrows dow to cities in Spain.
Here are some links on conditional value lists and the last one discusses hierarchical conditional value lists...
There's a lot of overlap between the first two links so you can read one and skim the other. The demo file gives you several examples of different conditional value lists so you can examine them to see how they are set up. If you are using FileMaker 12, you can open this demo file from your File menu to get a converted copy of the demo file that you can examine in FileMaker 12.
The last link discusses how to set up a chain of conditional value lists where the value selected in each conditional value list controls the values listed in the next value list.
Forum Tutorial: Custom Value List?
Knowledgebase article: http://help.filemaker.com/app/answers/detail/a_id/5833/kw/conditional%20value%20list
Hierarchical Conditional Value lists: Conditional Value List Question
Feel free to post follow up questions here if those links aren't enough to get your value lists working correctly.