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Ordnance Survey – Great Britain's national mapping agency

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A guide to coordinate systems in Great Britain

This guide can be considered essential reading for anyone trying to work with coordinates in Great Britain. It is a gentle introduction and an excellent source of information on the often confusing subjects of GPS and Ordnance Survey coordinate systems.

The guide is also the user guide to the companion coordinate utility spreadsheet.

A PDF version of the whole guide is available. To get a link to download Adobe® Acrobat® Reader

1. Introduction
2. The Shape of the Earth
3. What is position?
4. Modern GPS coordinate systems
5. Ordnance Survey Coordinate Systems
6. From one coordinate system to another: geodetic transformations
7. Transverse Mercator map projections
8. Further information

Annexe

A. Ellipsoid and projection constants
B. Converting between 3-D Cartesian and ellipsoidal latitude, longitude and height coordinates
C. Converting between grid eastings and northings and ellipsoidal latitude and longitude
D. Glossary