Google's local listings show for some listings the number of reviews left by a specific reviewer in a particular location. So if a specific person left 15 reviews and those reviews are for businesses within a particular city, Google may show that.
The example below is from Darren Shaw, he posted a screenshot showing how it shows by the reviewer's name how many reviews they left in a specific city. In this case, Selleck left 15 reviews in Edmonton and Berna left 36 reviews in Edmonton.
Darren said this is "very helpful to assess the legitimacy of the reviews."
Forum discussion at Twitter.
