From Geohashing

The Antimeridian is the 180th meridian. It is located simultaneously at 180° east and 180° west. It is a line going from the North Pole through the Arctic Ocean, Russia, the Pacific Ocean, Fiji, the Southern Ocean and Antarctica before reaching the South Pole.

In physical geography, this locale or set of locales is diverse but otherwise not particularly odd other than crossing a lot of ocean. In human geography, however, and in chronology, it is a fascinatingly strange literal edge case, delimiting the longitudinal sides of Mercator and similar projections (see osmwiki:180th meridian) and is the guiding longitude for the International Date Line, although it often deviates from it. Since geohashing concerns itself with both space and time, each kind of oddness applies.

The Antimeridian does not have any graticules in the traditional sense, since it is impossible for a geohash to fall on the longitude 180° + offset, unless this offset is exactly zero, since nothing can be further west than 180° west nor further east than 180° east. But it is possible to view the Antimeridian as several one-dimensional graticules.

In accordance with the Algorithm, there is a non-zero chance for the offset being zero. This to happen, the last sixteen digits of the MD5 Hash all have to be zero. The chances for this are 1616, and with two new values per day this means it will happen 25 times every 1015 years, which is a lot more than the current age of the universe.

Should a geohash ever fall on the Antimeridian, it would not just be one, but 180 geohashes all along this meridian. The Globalhash would also fall on the Antimeridian.

In addition to the South Pole and the North Pole, the Antimeridian borders 180 graticules to the west and 180 graticules to the east: