Date: 2007-05-17 13:44:00
locus of antipodes
I was thinking this morning about what exactly "the other side of the planet" means. In particular, how many places on the Earth have land on exactly opposite sides of the planet?

While home today with a nasty cold, I thought I'd pull out some trusty mapping software and have a go. The map below shows the earth in a Mercator projection, with points where there is land on exactly opposite sides shown in red. The amount of overlap is surprisingly small - even the largest continents have almost no representation on the other side.

Antipodes of the Earth

At first I thought there might be a mechanical reason for this apparent lopsidedness, something to do with balancing a spinning globe. However, thinking back in the history of the earth, Pangaea was one large supercontinent that plate tectonics broke up into the continents we know today. With the continents still shifting around, there would seem to be no particular reason why they might not line up across the globe from one another sometime in the future.

We can also examine this result statistically. The oceans occupy about 70% of the earth's surface, while land occupies about 30%. That means we should see about 9% (0.3 × 0.3 = 0.09) of the land cover having land on the other side. The actual number is about 8.4%, so really it's not too far from the expected value.
Heh, clever. I'm surprised I've never seen such a map before (that I can recall). It seems such a natural idea in hindsight. :)
Thanks. I always wondered about this, but wondered on a level that didn't quite spur me to research further.

I guess my childhood attempts at digging a hole to China would have only ended in tears.
[info]ivo : I KNOW I KNOW I KNOW!
I think I have the answer to today's geopoliticonomic question! "Which parts of the globe have a counterpart of land on the opposite side of the globe".

But seriously. You should repeat this graph without Antartica, and it's even worse (just South American and China). The fact is that almost all land is on the Northern Hemisphere.
en Interesting idea. I would chose an different projection though, since Mercator preserves shapes at the cost of hugely exaggerating areas at high latitudes. So it looks like all red is in Antarctica and Greenland when it's not really true in terms of square meters. Gall-Peters projection aims at preserving areas (but on the hand distorts shapes more). But since this is all about areas here, it would make sense.

eo Interesa ideo. Tamen, mi elektus alian projekcion, ĉar Mercator konservas formojn sed troigas areojn je altaj latitudoj. Pro tio ŝajnas, ke la plej parto de la ruĝa koloro estas en Antarkto, kaj en Groenlando, sed ne tiom veras aree. La projekcio Gall-Peters celas konservi areojn (sed tion farante pli ŝanĝaĉas la formojn). Sed ĉar temas pri areojn tie, pli taŭgus.
Greg Hewgill <>