Google My Business updated their help file page: “Improve your local ranking on Google” Page. And surprisingly, after a slow start, actually added some real ranking information (this does not appear to be a April 1 Joke):
Prominence is also based on information that Google has about a business from across the web (like links, articles, and directories). Google review count and score are factored into local search ranking: more reviews and positive ratings will probably improve a business’s local ranking.
Your position in web results is also a factor, so SEO best practices also apply to local search optimization.
I am archiving the page as a PDF for future reference.Google My Business Updates "Improve your local ranking on Google" Page by Mike Blumenthal