I'd start by mapping out all the options and seeing what they cost you in time and money (eg: are you techical enough to code this up in your sleep, or is it easier for you to pay someone).
Optons:
1) like Shaun said. map it using https://www.mapcustomizer.com/ or http://mapjam.com/
2) getting a quote on https://www.upwork.com/ for a human to do it for one city first to see the ROI.
3) plug in a street address of a store into yelp as 'near' field and type in opthamologist.

After testing each one for one city, you can decide if you want to automate it or just scale the option up.

Feel free to schedule a call with me.