Geography of the International Date Line

Elizabeth Borneman


The International Date Line is located at 180 degrees east or west of the Greenwich Meridian and is an imaginary line of longitude that differentiates between two different days. This is to account for the many time zones around the world to make it easier for people to know what time it is in various countries and to keep days uniform based on daylight hours.

The International Date Line separates two different days as the world turns.

When was the International Date Line developed?

The International Date Line was conceived of in 1884 at the International Meridian Conference in Washington, D.C. The conference was convened at the request of the President of the United States to determine an international time zone standard as the world began becoming more and more globalized.

The 24 hour clock was mapped around the world to create time zones and some details of what the date line would accomplish were discussed, although the exact geography of the date line wasn’t emphasized.

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Shade relief globe showing the International Date Line.
The International Date Line passes through the Pacific Ocean at about 180 degrees longitude. Map: Caitlin Dempsey.

This has led to the movement of the date line in some cases at the behest of nations most affected by it. In the present day computers couldn’t sync together, people couldn’t reliable communicate with one another and schedules would be thrown out of whack without strict adherence to time zones and the existence of the International Date Line.

What does the International Date Line look like?

The date line doesn’t follow a straight longitudinal path around the world. The date line separates two consecutive calendar days which accounts for a gain or loss in a day when traveling around the world.

The International Date Line has had to be amended as it passed through countries and cities who found it easier to be on the same time. Countries that were split by the International Date Line were often left up to their own devices when it came to changing time zones or instituting different practices for dealing with the date line mishaps.

Map showing the International Date Line.  Source: Jailbird, GNU Free Documentation License, Wiki Commons, 2014.
Map showing the International Date Line. Source: Jailbird, GNU Free Documentation License, Wiki Commons, 2014.

The development of time zones around the world

Throughout the existence of the date line countries have merged time zones and changed the boundaries of the date line to make things easier. For instance, China instituted a one time zone policy instead of its previous 5 to unify country in 1949; the practice has continued to the present day.

Russia also turned its eleven time zones down to 9 making it easier for the more populated parts of the country to work with the lesser populated areas in the north and east.

Some countries or cities choose to leave themselves in the middle of the International Date Line or a time zone; a city in Indiana, for instance, is located across two time zones! There are many reasons why a nation might choose to alter the International Date Line around its borders; politics, logistics, unity and more.

The implementation of the International Date Line hasn’t always been smooth.

When countries decide they want to change the date line to encompass their country or move it entirely out of the way they have to inform the public, inform cartographers to change maps, and tell the international community. Often this involves skipping a day, as the island of Tokelau did in 2011. Samoa skipped a Friday when it adjusted the International Date Line to make it easier to do business with its major trading partner, Australia.

German map of the International Date Line in 1872 showing the separation between Sunday (Sonntag) and Monday (Montag).  Source: Wiki Commons.
German map of the International Date Line in 1872 showing the separation between Sunday (Sonntag) and Monday (Montag). From Die Gartenlaube. Source: Wiki Commons, public domain

Not everyone adjusts to the International Date Line changes that have been made. Maps are still drawn with conflicting reports of where the line sits around the world, and critics think that the date line should be governed by an international body as it does affect how the entire world relates to one another. However, there are few hardliners when it comes to the International Date Line and the changes that nations like Samoa or Russia make to it to make their business run easier in the grand scheme of things.

The International Date Line helps regulate time zones, nations, and the ways in which people communicate around the world. Businesses couldn’t run without the International Date Line, and travelers would have a hard time buying tickets or catching their planes and trains if time zones weren’t well documented!


Lane, Megan. How does a country change its time zones? BBC News. 10 May 2011. Web access 15 February 2015.


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About the author
Elizabeth Borneman
My name is Elizabeth Borneman and I am a freelance writer, reader, and coffee drinker. I live on a small island in Alaska, which gives me plenty of time to fish, hike, kayak, and be inspired by nature. I enjoy writing about the natural world and find lots of ways to flex my creative muscles on the beach, in the forest, or down at the local coffee shop.