Great Britain National Grid


This is a Transverse Mercator projected on the Airy spheroid. The origin is 49° N and 2° W. The central meridian is scaled to 0.9996012717. The value changed at version 9.2. The earlier value was 0.999601272. Because of this change, if two datasets have the different scale factor values, they are not considered equal. In version 9.3, the code was changed to treat both values as equivalent.

Learn more about Transverse Mercator projection

Illustration of the Great Britain National Grid coordinate system

Projection method

Cylindrical, transverse projection with the central meridian centered along a particular region.

Lines of contact

Two lines parallel with and 180 km from the central meridian at 2° W.

Linear graticules

The central meridian.



Conformal; therefore, small shapes are maintained accurately.


Distortion increases beyond Great Britain as the distance from the central meridian increases.


Local directions are accurately maintained.


Scale is accurate along the lines of secancy 180 km from the central meridian. Scale is compressed between them and expanded beyond them.


Suitable for Great Britain. Limited in east–west extent.

Uses and applications

The national coordinate system for Great Britain; used for large-scale topographic mapping.



  • Projection-specific parameters are set by the software.

Related Topics