Coordinate Reference System (CRS)
Overview
Coordinate Reference System (CRS) is a system that uses coordinates to establish a position in space, allowing for the accurate mapping and analysis of geographic data. A CRS defines the origin, units, and axes of a coordinate system and relates them to real-world locations on the Earth’s surface.
Key Concepts
Geographic CRS uses angular units (degrees) on a three-dimensional ellipsoidal model of the Earth (latitude/longitude). Projected CRS uses linear units (meters, feet) on a two-dimensional flat surface created by mathematical projection. Datum is the reference surface and origin point for a coordinate system. Ellipsoid is the mathematical model approximating the Earth’s shape. Projection is the mathematical transformation from 3D geographic to 2D planar coordinates. EPSG code is a standardized numeric identifier for coordinate reference systems.
Types of Coordinate Systems
| Type | Coordinates | Units | Use Case |
|---|---|---|---|
| Geographic | Latitude, Longitude | Degrees | Global data, GPS |
| Projected | Easting, Northing | Meters/Feet | Local mapping, area calculations |
| Local | X, Y | Various | CAD, engineering |
Common CRS Examples
- WGS 84 (EPSG:4326): Global geographic standard, used by GPS
- Web Mercator (EPSG:3857): Web mapping (Google Maps, OpenStreetMap)
- UTM Zones: Regional projected system with minimal distortion
- State Plane: High-accuracy projections for US states
Appendix
Created: 2025-12-13 | Modified: 2025-12-13