2. Longitude is dihedral angle, that is, the included angle between two meridian planes. Because all meridians are the same length, choose a starting point to measure longitude. After consultation at the 1884 international conference, it was decided that the starting meridian was the meridian crossing a main meridian cross at the Royal Greenwich Observatory (former site) on the south bank of the Thames in London, England. The prime meridian plane is the starting point plane and the ending point plane is the local meridian plane. The longitude of a point is the angle between the meridian plane where the point is located and the prime meridian plane. Measured on the equator, from the prime meridian plane as the starting point plane, measured to the east and west respectively. The east value is called east longitude and the west value is called west longitude. It can be seen that the longitude of a place is its direction and angular distance from the prime meridian. The prime meridian is zero longitude, the maximum longitude is east longitude 180, the maximum longitude is west longitude 180, and the longitude of east longitude 180 is the same meridian, so both east longitude and west longitude are called 180 longitude.
3. Latitude is the line angle. The starting point plane is the equatorial plane and the straight line is the local ground normal. The so-called normal is a straight line perpendicular to the reference oblate sphere. The latitude of a place is the angle between the normal and the equatorial plane. Latitude is measured on the local meridian, from the equator to the north, the northern value is called north latitude, and the southern value is called south latitude. It can be seen that the latitude of a place is its direction and angular distance from the equator. The equator is latitude 0, and the maximum north latitude is 90, which is the North Pole. The maximum south latitude is 90, which is the South Pole.