I've been doing SEO since around January 1993 when we used to rank music and nightclub events on AOL Bulletins.. Then I used to figure out how to get things listed prominently in MySpace. Yahoo Directory was a good friend, when it was free, then $199 then $299. Then we had Dmoz.org. My volunteer position was to determine directory structure of Business/ Health/ Shopping/ and /Law.
However each one also had a service area or some type of location.. it may have been a Plastic Surgeon which meant it was listed in /Plastic_Surgeons but those also needed to be listed and sorted by Where they were as well. In the 90's Local was a factor in search in Yahoo! Directory as well as Webcrawler. Google was still Backrub. Anyways..
Each one of these had a sub-category - Regional/North_America/United_States/Texas this is how Google's Search Engine now begins to "Classify and Categorize" Local results.. eventually it breaks down to County, City and ZipCode. Those also have Regions with them, in Texas we have the "PineyWoods" (East Texas) and Hill Country (Austin and Central Texas) this is called a "sub-classification" or secondary grouping.
When you search for a Veterinarian in Plano, Texas. How many different ways can you think to classify or categorize that listing.. What are the "attributes" involved with that Local listing?
2016 SEO Lesson #1 - write what you just thought down. As your brain "Classifies and Categorizes" the "listing".