Unfortunately we were wrong. It is really rather uninteresting.
Don't even look at this map showing the absolute number of mentions of grocery stores in the Google Maps directly. It simply shows that they are everywhere that people are. DON'T LOOK!

Even when we normalize the data to create a measure of grocery store specialization, we end up with a big YAWN. Urban areas have more grocery stores per capita than rural areas.

No doubt tied to the higher division of labor (e.g., more specialty grocery stores) that large centers of population have as well as the fact that urban areas have higher land costs and fewer available large parcels that results in a built environment of more (albeit smaller) establishments.
Wow… it's rather sad that we spent as much energy as we did to create this. It's boring. Much like the act of shopping for groceries. But like grocery shopping, it needs to be done. But hopefully by someone else, next time.
Apologies all around. Next post we'll show more interesting like urban maps of user generated references to crime or distribution of escort services…stay tuned.