# Geographic coordinates

##### Article

July 6, 2022

Geographic coordinates are values ​​that determine the position of a certain point on the terrain (on a plan or on a topographic map) relative to the adopted coordinate system. The coordinate system establishes the starting (starting) points of the surface or the reference line of the required values ​​— the starting point of the coordinates and the units of their calculation. The geographic coordinate system and the flat rectangular coordinate system are presented on topographic maps. The system of geographic coordinates (geographic coordinates) is used to determine the position of points on the Earth's surface relative to the equator and the prime (zero) meridian. Coordinates are angular values: geographic latitude B and geographic longitude L. The minute frame is used to determine geographic coordinates on topographic maps. Longitude (the angle between the meridian plane at the point of observation and the zero (Greenwich) meridian), Latitude (the angle between the vertical line and the plane of the equator) determine the position of the point on the Earth's surface. Measured in degrees (°), longitude — from -180° to 0 west and from 0 to 180° east of Greenwich, latitude — from 0° to 90° north, from 0° to −90° south of the equator . Geographic coordinates convey the horizontal (plan) position of points. But when working with a topographic map, it is necessary to know the absolute height. Absolute heights in Ukraine are determined in the Baltic system of heights (relative to the surface of the geoid). To ensure the correct position of objects on the map, it is necessary to determine the geographic latitude and geographic longitude and absolute height of a certain number of points, and the position of all others - relative to these. Points fixed on the terrain with precisely established plan and height coordinates are called reference points, which are divided into points of the plan base and points of the height base. A set of reference points gives a reference geodetic network. The accuracy of determining the coordinates of reference points affects the accuracy of the geodetic base of the map.

## History

The invention of the geographic coordinate system is usually attributed to Eratosthenes of Cyrene, who compiled his now lost "Geography" in the Library of Alexandria in the 3rd century BC. e. A century later, Hipparchus of Nicaea improved this system, viz�