Place one slice of bread on the ground. Good! Now, at the same time, ask someone at the exact opposite side of the planet to place another slide of bread on the ground where they stand. Congratulations! You have just created an Earth sandwich.

It may seem silly, but quite a lot of time and attention has been expended by people trying to create their own Earth sandwiches, ever since blogger Ze Frank issued the challenge in 2006. For the adventurous cartography nerd, it’s just the sort of challenge to accept.

The key for anyone aspiring to fix an Earth sandwich is to determine the location of the antipode for their current location. The antipode is the direct opposite of a certain coordinate on the earth’s surface. If you drilled down into the center of the Earth and kept going until you reached the other side, you will have found your antipode. Unfortunately, it’s much harder than it may seem to even find suitable locations, given the amount of ocean that covers the Earth’s surface. Many of us who grew up in the US believed as kids that if we dug straight through the Earth we’d wind up in China (and Bugs Bunny cartoons did their part in reinforcing this). In reality, though, the antipode of any location in the continental US is somewhere in the Indian Ocean.

The following map, courtesy of Mr. Reid’s blog, shows the earth flipped upside down and laid over itself, so you can see where land overlaps in green. These are the only locations where an Earth sandwich can be successfully assembled.

A whole lot of the world is, sadly, out of luck when it comes to making their own Earth sandwich. Residents of North America will have to travel to the Canadian Arctic to lay a slice of bread upon the ice, and have a friend in Antarctica do the same. Or they can head down to South America, where significant areas of countries such as Chile, Argentina, Brazil, and Peru overlap with Asian countries like China, Cambodia, and Vietnam.

There are a few other interesting antipodes as well. Look at the Iberian peninsula in Europe and you will see a couple splotches of green. These match up with the islands of New Zealand way in the South Pacific. In fact, as Ze Frank reports, the very first Earth sandwich in the world was created at these locations, with one side near Madrid, Spain and the other near Aukland, New Zealand. Pretty cool!

The mere existence of the Earth sandwich shows the depth of imagination which map nerds share. Sure, the sandwich can’t be eaten, but to a geography obsessive, it satisfies a different kind of hunger.

For more on the Earth sandwich, check out Ze Frank’s page here: http://www.zefrank.com/sandwich/