We live on a sphere. Wherever you are, some 8,000 miles directly beneath you is the other side of the planet. That location is your antipode. It seems strange to think of it being there, completely upside down and yet completely normal to its inhabitants. Who might that be? Finding the exact location is an easy spatial problem to solve.
Any two points that are diametrically opposite each other are antipodal. The antipode of any location is 180º away in longitude and exactly the same distance from equator in the opposite direction. This simple calculator does the math for you. Start with any valid coordinate pair in decimal degrees. Or, to make it easy, you can just use the location of your IP address.
North Americans tend to think that China is on the other side of the world, but it's not. People elsewhere may have similar misconceptions about their antipodal neighbors. We'll use the ThereAbout web service to find out what's really there:
Surprised? Chances are extremely good that your result was open ocean. That's partly due to the fact that about 71% of the Earth's surface is water. More amazingly, less than 5% of it is antipodal land. The largest such areas are the countries of Argentina and Chile which are almost entirely antipodal to China and Mongolia. Indonesia is antipodal to the Amazon basin and Greenland is largely antipodal to Antarctica. There are very few other places where there is land on both sides of the world.
The only significant antipodal land in the United States is Hawaii, which lies opposite the African nation of Botswana. The Arctic coasts of Alaska and Canada as well as the Canadian Arctic Archipelago are opposite Antarctica. If you are near Medicine Hat, Alberta, you are antipodal to the large and mysterious island of Kerguelen. The towns of Shellbrook in Saskatchewan and Lamar and Cheyenne Wells in Colorado, are near the antipodes of three much smaller specks of land; Heard Island, Île Amsterdam and Île Saint-Paul (respectively). Otherwise, there is only water beneath the entire continent of North America. Australia has a similar relationship to the North Atlantic, Africa to the Central Pacific and Asia, for the most part, is opposite the Southern Atlantic and Pacific Oceans:
This arrangement is sometimes call the "antipodal balance" because land and sea are so evenly distributed around the globe. The exact reason for this (if there is one) is not clear. In 1875 Lowthian Green observed that the distribution of the Earth's crust is tetrahedral. A tetrahedron is a solid body having the least volume compared to its surface area. A sphere has the most. So, Green theorized that the cooling of the primordial earth caused the surface to become lower on four sides corresponding to the major oceans we see today. This idea has since been supplanted by Alfred Wegner's theory of continental drift (1912), but it is still an interesting hypothesis.
The term "antipode" comes from Greek for "opposite feet" and it was first used by Plato in describing the relative perspectives of people on opposite sides of the planet. Scholars of the Middle Ages speculated that the antipodes could not be reached because of the torrid climate that must surely pervade the equator. They were right-thinking though, in some respects. A Norwegian text from around 1250 suggested that the sun there would transit the northern sky and the seasons would be opposite.
As global exploration opened up the far reaches of the planet, the notion of being above and/or below another place on Earth continued to intrigue geographers. There is, in fact, an small uninhabited island named "Antipodes" some 500 miles southeast of New Zealand. It was originally called "Panantipodes" by its British discoverer since it is near the antipode of London, England. The name has since been shortened, leading some to think that Capt. Waterhouse (HMS Reliance) had mischarted it in 1800. He did not. I suspect he was simply loath to mention that it is actually antipodal to the coast of Normandy in France.
Antipodes seem to have a particular significance for humans. Perhaps that is because a pair of antipodes are as far from each other as any two places can possibly be in this world. The "ends of the Earth", if you will. That is certainly one way to measure the limits of our existence.