Here’s where a “metro area” comes from, straight from Wikipedia:
In the United States, a metropolitan statistical area (MSA) is a geographical region with a relatively high population density at its core and close economic ties throughout the area. Such regions are neither legally incorporated as a city or town would be, nor are they legal administrative divisions like counties or separate entities such as states. As such, the precise definition of any given metropolitan area can vary with the source. A typical metropolitan area is centered on a single large city that wields substantial influence over the region (e.g., Chicago or Atlanta). However, some metropolitan areas contain more than one large city with no single municipality holding a substantially dominant position (e.g., Dallas–Fort Worth metroplex, Riverside–San Bernardino or Minneapolis–Saint Paul).
MSAs are defined by the Office of Management and Budget (OMB) and used by the Census Bureau and other federal government agencies for statistical purposes
So who sets the MSA is the OMB at the Federal Government. If they cay it’s the metro, then it’s the metro – I don’t think you have any input into it.
Your test ad should tell you of the demand in your area from this MSA. I would go by that.