
The folks over at City Observatory have recently developed something called The Storefront Index.
It is a mapping of “clustered” consumer-facing storefront businesses across the 51 largest cities in the United States and within a 3-mile radius of their CBD. (Their definition of cluster is that the business is located within 100m of another business.)
At the top of this list is New York (no surprise here) with 9,905 storefronts and at the bottom of this list is Detroit (probably no surprise here either) with 411 storefronts. On average, they found that the “typical” city has about 900 storefronts within this 3-mile radius.
Here’s a screenshot of New York:

