What fast food chain has the most restaurants around the world? Most people think the answer to this question is that archetype of the fast food industry, McDonald's. But in terms of total outlets, it's actually Subway.

Subway has over 27,000 locations in the U.S. and around 43,000 locations worldwide, compared to 36,000 globally for the golden arches. In the U.S., Subway had more locations than Starbucks and McDonald's combined in 2013.

Subway has been rapidly expanding for a while, opening more than 2,000 new locations per year for the past 10 years. The company can do this in part because its shops have a much smaller footprint than competitors like McDonald's -- as little as 300 square feet. This allows Subway to grab up space in shopping and strip malls, but also hospitals, airports, colleges, gas stations and sports venues.

Subway also has a much bigger lead on other sandwich chains than McDonald's does on its burger-flipping competitors, as a new series of maps by Nathan Yau, who runs the blog Flowing Data, show. Using sandwich data from AggData, Yau mapped sandwich chains with at least 100 locations around the U.S.. Each dot represents an area with a 10-mile radius, colored by the nearest sandwich chain.

Here are the chains mapped separately (click on the graphic to see an expanded version):

And here they are combined in one map. Chains like Arby's, Panera Bread, Quiznos, Jimmy John's, Blimpie and Potbelly show up here and there, but Subway has twice as many locations as all other sandwich chains in the U.S.:

And here's what the map looks like without Subway:

In comparison, Yau's map of burger geography shows that McDonald's faces a lot more competition.

Yau has made similar maps for pizza places, coffee shops and grocery stores. You can see those on his site.

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