Hello! Tawny from Moz's Help team here.
Unfortunately, it's a bit more complicated than just adding in a new location to our database.
The locales are tracked as a defined region with borders established by Google. It's hard to say exactly how Google is defining these areas, but it is likely related to ZIP codes and IP addresses.
I found this article while I was researching — it doesn't have exact answers to this question either, but had some valuable insight into Google's local search results: http://searchengineland.com/everything-need-know-pigeon-algorithm-211771. Section 7 of this resource would be the most relevant to how those locations are defined.
The locales we include in Moz Pro are specific to the Google search engine only, and our list is based on a finite postal code database, so you may not see every locale you would like to track in the list. It is helpful to be very specific when entering the locale, and it can help to include a specific neighborhood, state, or county name when entering the locale (e.g.: Melbourne, Victoria vs. Melbourne, Australia).
That means you might see more specific areas than the Dallas-Fort Worth metropolitan area, but probably won't see locales as broad as an entire county.
If you still have questions we can help with, feel free to drop us a line at help@moz.com and we'll do our best to sort everything out. 
