# Projections in GIS

Projections or Map Projections are attempts to portray the 3D surface of the earth or a portion of the earth on flat surface like flat surface or XY plane or Cartesian Plane. The method by which 3D earth surface or curved surface is laid flat to a flat surface or XY plane is known as map projections.

In order to understand Map Projection, we need do understand Latitude and Longitude

Latitude and Longitude: Lets first discuss what is Equator and Prime Meridian. In the above figure, the earth is divided into parallel horizontal and vertical lines. The largest line that runs horizontally is known as Equator and the largest line that runs vertically is known as Prime Meridian. The point where Equator and Prime Meridian intersects is known as origin or centre of earth. Every Lat-Long of any location of earth are calculated with respect to this origin or centre of earth.

Every vertical and horizontal lines divide the earth in number of parts known as Degrees. Each vertical and horizontal lines composed of 360 degree angles. Each degree or part is composed of 60 minutes. Each minute is composed of 60 seconds

Latitude is calculated on Equator or horizontally and Longitude is calculated on Prime Meridian or vertically. Latitude and Longitude are used in Geographic Coordinate System where a location on earth is expressed as Latitude and Longitude.

Latitude and Longitude are the measures of angles from the centre of earth to a point or location on earth’s surface

Geographic Coordinate System(GCS): GCS is a reference framework that defines location of a point or feature on earth surface in the form of Latitude and Longitude or decimal degrees. Its units are angular.

Projected Coordinate System(PCS): PCS is flat or plane. It contains the Geographic Coordinate System but convert it into flat surface or XY plane using a mathematical formula or algorithm also known as projections. Its units are linear.