Greenwich mean time (GMT) is mean solar time at the Royal Greenwich Observatory in Greenwich, London, England, which by convention is at 0 degrees geographiclongitude.
格林尼治国际标准以英国伦敦格林威治皇家天文台为准，也就是零经度为准。
2
The coordinate values represent latitude and longitude: "geographic" coordinates, not projected ones.
坐标值代表纬度和经度：“地理” 坐标，不是投影坐标。
3
The latitude and longitude system is probably the best known way to designate geographic coordinates.