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This question on Politics.SE asks about the alignment of maps, and got two answers. The first (mine) says the split through the Bering Strait was chosen for practical reasons, the second says that it's due to centering on the Prime Meridian.

This led me to wonder whether the ease-of-splitting was a deliberate factor in choosing the Prime Meridian, or whether it coincidentally happened that halfway around the world was almost entirely ocean. Was this a factor, or just historical coincidence? The Wikipedia article makes it clear that it was chosen at the International Meridian Conference, and provides some reasons, but doesn't discuss this part at all.

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FWIW 180 degrees longitude doesn't actually pass through the Bering straight. It's close, but hits Russia. London is "good enough" that the international date line doesn't have to deviate so much as to be impractical. Just looking at the map, I reckon Paris would have been "good enough" too. –  Steve Jessop Aug 22 at 22:40
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Technically, the answer to the question in the title is "no". The location of the 180° line was neither coincidence or deliberate choice: it was an inevitable consequence of the choice of the prime meridian. ;-) –  David Richerby Aug 23 at 11:44

3 Answers 3

The Prime Meridian we use now was the one the British chose, since it went through Greenwich Observatory near London. France had their own where Paris was 0 degrees, the US had one.

When the situation of each nation having its own longitude got too annoying, they picked one. England's won out because of 2 factors:

1) England was the largest power at the time, with the largest Navy

2) The opposite meridian, where the date line is, fell almost entirely in mid-ocean in the Pacific, with a jog here or there. This coincidence helped seal the deal over a meridian based in Washington DC or somewhere, where the date line would pass through Asia.

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As an expansion of point 1), England also had the largest merchant fleet, and the best (or at least the reputation for the best) maps. –  Mark Aug 22 at 21:17
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This makes sense; do you have any references to support this? I don't mean that to sound challenging, just that it would be much better if it had a citation to rest on. –  Jon of All Trades Aug 22 at 22:34
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Isaac Asimov wrote a science essay about this in the 1970s –  Oldcat Aug 22 at 23:05
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France refused to recognize the Greenwich meridian for decades. And when they finally adopted GMT in 1911, the legislation described France's new timezone as "Paris Mean Time minus 9 minutes and 21 seconds" rather than GMT. –  dan04 Aug 23 at 1:37
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@NicolasBarbulesco: This nicely written page gives a lot of information (including the info in dan04's comment) and some references. –  Matt Aug 25 at 8:38

The book "Longitude" discusses this, and says the international standardization of the prime meridian arose mainly due to the publication of practical astronomical tables which used the Greenwich meridian. As ships started using these tables for navigation (as opposed to dead reckoning), they naturally switched to using the Greenwich meridian if they hadn't been using it already.

The location of 180° was not a factor. Even today, the international date line does not follow the 180° line very well, but rather takes a route to minimize confusing human interactions across the date line. For example, it deviates by almost 30° to allow Kiribati's Line Islands (which reach east of Hawaii) to be 14 hours off of Greenwich mean time. There is no need for the date line to be close to 180°, and there were even brief efforts (led by France) to have the prime meridian pass through the Bering straight.

Of course, the 180° line itself (which is not particularly more meaningful than any other longitude line) is by definition exactly opposite the 0° line, but nobody was choosing their 0° line based on that -- they were all choosing to put 0° through their nation's capital or whatever other location they found convenient for their calculations.

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The choice of the Greenwich Meridian (for the 0 degree longitude) was arrived at during a time when Britain was the primary naval power and London was the "center" of the world.

It is fortunate at the 180 degree line (relative to the Greenwich Meridian) mostly ran through the Pacific Ocean. That made it convenient to have much the international date line along that line. Except that it was "bent" in the far north to go through the Bering Strait, rather than through a piece of land, and "bent" further south to accommodate Hawaii.

France and America had their own 0 degree lines, but neither of them were as powerful at sea as Britain in the 19th century. And the line through Washington D.C. had the further disadvantage of its 180 degree divided Siberia and the rest of Asia in half.

So the British 0 (and by implication, 180 degree) line was adopted.

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I doubt that the line would have been bent for Hawaii. Hawaii is in west (american) longitude, like the continental USA. –  Nicolas Barbulesco Aug 27 at 10:43

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