# Components of a Geographical Coordinate System: Basic Components (Especially for GATE-Geospatial 2022)

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A geographic coordinate system has the following components:

## Basic Components

**Angular units**: The unit of measure on the spherical reference system.**Spheroid**: The reference spheroid for the coordinate transformation.**Datum**: Defines the relationship of the reference spheroid to the Earthีs surface.**Prime meridian**: The longitude origin of the spherical reference system.

## About the Components

The **angular unit** of measure is usually degrees, in which the unit represents one part in 360 of a circle. But it may also be grads, in which the unit represents one part in 400 of a circle.

The **prime meridian** defines the zero value for longitude. (It is not necessary to define a zero value for latitude, since this is always the equator)

The **datum** specifies the sphere or spheroid. It does a little bit more than that, but we will talk about the rest in the next module.

A sphere is defined by the length of its radius. A **spheroid** defined by the length of its semi-major and semi-minor axes or by the length of the semi-major axis and the flattening value. (Flattening, or the oblateness of the spheroid, is the ratio of the semi-major to the semi-minor axis.)