.svg/1280px-World_location_map_(equirectangular_180).svg.png)
The meridian 100° west of the Prime Meridian of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole. The 100th meridian west forms a great circle with the 80th meridian east.
In the United States, this meridian roughly marks the boundary between the semi-arid climate in the west and the humid continental and humid subtropical climates in the east and is used as shorthand to refer to that arid-humid boundary.
The meridian coincides with the approximate center of the continental United States, and is featured prominently on the cover of the Charter of the United Nations.
Starting at the North Pole and heading south to the South Pole, the 100th meridian west passes through:
In the United States the meridian 100° west of Greenwich forms the eastern border of the Texas panhandle with Oklahoma (which traces its origin to the Adams-Onís Treaty in 1819 which settled the border between New Spain and the United States between the Red River and Arkansas River). Dodge City, Kansas lies exactly at the intersection of the Arkansas River and the 100th meridian.
As first noted by John Wesley Powell in the 1870s, there is a big difference in rainfall by the different sides of the meridian. In the central Great Plains, it roughly marks the western boundary of the normal reach of moist air from the Gulf of Mexico, and the approximate boundary (although some areas do push the boundary slightly farther east) between the semi-arid climate to the west and the humid continental (north of about 37°N) and humid subtropical (south of about 37°N) climates to the east. West of the meridian, raising livestock is much more economically important than east of it, and what agriculture does exist relies heavily on irrigation. Historically, the meridian has often been taken as a rough boundary between the eastern
.svg){kind=link}