The west longitude (W) is the part from the west of the 0 meridian (prime meridian) to the180 meridian; Longitude from 0 to 180 is east longitude (e); 20 W to160 e is the eastern hemisphere; 20 W to160 e to the west is the western hemisphere.

Meridian 0-internationally, the meridian passing through the original site of Greenwich Observatory in London, England is designated as meridian 0, also called prime meridian. From this line to the east (to the right), the longitude gradually increases to 180. From the 0 meridian to the west (to the left), the longitude gradually increases to 180.

Extended data:

Longitude refers to the dihedral angle formed by the meridian plane passing through a place and the prime meridian plane. The longitude east of the prime meridian is called east longitude, and the longitude west of the prime meridian is called west longitude. East longitude is represented by "e" and west longitude by "w". The eastern and western hemispheres are divided into the eastern and western hemispheres by longitude 20 degrees west longitude and longitude 160 degrees east longitude.

According to international regulations, the meridian passing through the original site of Greenwich Observatory in London, England is designated as 0 meridian, also called prime meridian.

Starting from longitude 0, the east and west are divided into 180, the east of 180 belongs to east longitude, and it is customary to use "e" as the code name, and the west of 180 belongs to west longitude, and it is customary to use "w" as the code name. East longitude 180 and west longitude 180 coincide on a meridian, that is, longitude 180.

References:

Baidu encyclopedia-longitude

Baidu encyclopedia-east longitude