# Geographic coordinate system

The location of every point on the Earth's surface can be clearly determined by the two coordinates of the geographic coordinate system.

## First and second dimensions: latitude and longitude

A point P on the surface of the sphere can be given by the latitude of φ and the longitude of λ. Originating from the ancient Babylonians and later expanded by the Greek thinker and geographer Ptolemy, the entire circle can be divided into 360 degrees (360°). Based on this, the special spherical coordinate system used in geography can be created.

## Latitude

(φ): The width of the point P is obtained by connecting it to the center of the Earth, and the angle formed by the line thus obtained and the plane of the Equator gives the width. By agreement, the sign of the value is positive in the north direction and negative in the south direction.
The line formed by points of the same width is the circle of latitude. The planes of latitude are parallel to each other and to the Equator. The Equator (φ0) is the longest latitude, the latitudes shorten towards the poles. The poles are located at 90 degrees: North Pole: +90°; South Pole: -90°.

## Longitude

(λ): the angle of the meridian plane of a point with the initial meridian plane (by convention, positive in the east direction, negative in the west direction). The meridian plane of the point is the plane that contains the two poles and the point.
The curve formed by points of the same length is the meridian, also known as the circle of longitude. The initial meridian (λ0) passes through an arbitrarily selected point on the Earth's surface, the Greenwich Observatory (Royal Observatory, Greenwich). The antimeridian is 180° east and west of the prime meridian. Unlike latitudes, meridians are of the same length and not parallel: they all pass through the north and south poles.

## Idealistic coordinate system

By specifying these two angles, the horizontal position of any place on Earth can be described. The positive and negative directions of the angles are often indicated by the initial letters of the English skyscapes (N, S, E, W).
The center of the Chain Bridge, for example, is located in Budapest at 47.498970 degrees north latitude and 19.043604 degrees east longitude, i.e. at 47 degrees 29 minutes 56.29 seconds north latitude and 19 degrees 2 minutes 36.97 seconds east longitude. (N. 47° 29′ 56″, E. 19° 02′ 37″47.498969444444, 19.043602777778)
The set of latitude and longitude circles is the general degree network. There is also a transverse (transverse) grid of degrees, by turning the grid of degrees by 90°, i.e. where the poles are on the horizontal Equator, which is also based on the spherical surface coordinate system.
Conventionally, angles are divided into degrees (°), minutes ('), and seconds ("). However, there are many other formats for angles, each in latitude-longitude order.
For example:
DM (Degree:Minute) Degree:Minute (49:30.0-123:30.0)
DMS (Degree:Minute:Second) Degree:Minute:Second (49:30:00-123:30:00)
DD (Decimal Degree) Decimal degree (49.5000-123.5000), usually up to 4 decimal places Conversion from DM or DMS to DD, Decimal degree whole number of degrees + number of minutes divided by 60 + number of seconds divided by 3600. Decimal division of degrees is currently the most commonly accepted standard.
The Equator is obviously an important part of this geographic coordinate system because it represents the zero point of the latitude angle and is halfway between the poles. The equator is the base plane of this geographic coordinate system. A similar base plane must be defined for each spherical coordinate system.

## Realistic coordinate system

The actual latitude and longitude coordinates are