Spatial Reference Systems: Definitions

Spatial Reference Systems (SRS)

Spatial Reference Systems, also referred to as "Coordinate Systems" or "Coordinate Reference Systems", include two common types:

• Geographic Coordinate Systems
• Projected Coordinate Systems

Try not to confuse this with the more general terms:

• Spherical Coordinate System
• Rectangular Coordinate System

Esri uses the following terms interchangeably to refer to a spatial reference system:

• Coordinate System
• Spatial Reference System
• Projection (and "prj")

Geographic Coordinate Systems (GCS)

Geographic Coordinate Systems consist of:

• Datum
  • Ellipsoid
    • Major Axis
    • Inverse Flattening
• Prime Meridian (Greenwich)
• Units (Degrees)

Projected Coordinate Systems (PCS)

Projected Coordinate Systems consist of:

• Geographic Coordinate System
• Projection Method
• Parameters
  • Number varies with the method
• Units
  • Always linear

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