Amazon made headlines last week when it announced that it was bringing its one-hour delivery service, which was previously only available in Manhattan and Brooklyn, to Miami and Baltimore.

Besides its three one-hour delivery locations, Amazon also offers same-day delivery in nine other markets. As you'd expect, Amazon offers this service in regions where it already has fulfillment centers.

To get an idea of where Amazon might expand to next, research firm Piper Jaffray created a map that shows all of Amazon's fulfillment centers in the US as well as its existing same-day shipping regions (represented as blue pins, some of which are hard to see under the red fulfillment center pins).

Here's the map, via Piper Jaffray:

Piper Jaffray

In case you can't tell, Amazon currently offers same-day shipping in New York City, Atlanta, Baltimore, Boston, Chicago, Indianapolis, Philadelphia, Washington D.C., Dallas, Los Angeles, Phoenix, San Francisco, and Seattle. The map hints that Florida, Tennessee, and Virginia could each make good same-day delivery expansion targets.

Right now, Piper Jaffray analysts estimate that the locations of Amazon's fulfillment centers bring it within 20 miles of 31% of population, but within 20 miles of 50-65% of its core same-day addressable market (Jaffray came to this higher percentage by predicting that only households with an annual income of $50,000 would be interested in same-day delivery).

As more brick-and-mortar retailers start offering in-store pick-up, Amazon's expansion of its same-day and same-hour delivery help it build "defensive moats" around its own offerings, the firm writes.