LogoLogo
OS Docs HomeOS NGDOS APIsOS Download ProductsMore than MapsContact Us
  • More than Maps
  • Geographic Data Visualisation
    • Guide to cartography
      • Introduction to cartography
      • Types of maps
      • Symbology
      • Colour
      • Text on maps
      • Generalisation
      • Coordinate reference systems
      • Projections
      • Scale
      • Map legends
      • Map layout
      • Relief representation
      • North arrows
    • Guide to data visualisation
      • Introduction to data visualisation
      • GeoDataViz design principles
      • Types of visualisation
      • Thematic mapping techniques
      • Data visualisation critique
      • Accessible data visualisation
      • Ethical data visualisation
      • Software
      • Data
    • GeoDataViz assets
      • GeoDataViz basemaps
      • Stylesheets
      • GeoDataViz virtual gallery
      • Equal area cartograms
      • How did I make that?
        • Apollo 11 Landing
        • North York Moors National Park, 70 years
        • Snowdonia National Park, 70 years
        • Great Britain's National Parks
        • Great Britain's Islands
        • Great Britain's AONB's and National Scenic Areas
        • Famous shipwrecks of Pembrokeshire
        • Trig pillars today
        • Britain's most complex motorway junctions
      • #30DayMapChallenge
  • Data in Action
    • Examples
  • Demonstrators
    • 🆕Product Viewer
    • Addressing & location demonstrators
      • Address Portfolio overview
      • Which address product should you use?
      • AddressBase
      • AddressBase Core
      • AddressBase Plus
      • AddressBase Premium
      • Address Classifications
      • Addressing Lifecycle
      • OS Emergency Services Gazetteer
      • What are Vertical Streets?
      • Why are there differences in boundaries?
    • Contextual demonstrators
    • Customer best practice
      • Channel Shift
      • Data Management and OS Data Hub
      • End User Licence vs Contractor Licence
      • 🆕 IDs vs Spatial Relationships
      • Why we should capture good quality addresses at source
      • Why we Snap and Trace
    • Network Demonstrators
      • OS Detailed Path Network
      • OS Multi Modal Routing Network
        • OS Multi Modal Routing Network
      • Water Networks overview
      • OS MasterMap Highways Network and OS NGD Speeds
      • OS MasterMap® Highways Network and OS Open Roads™
    • OS MasterMap Generation APIs
      • Using the OS Features API
      • Using the OS Features API Archive
      • Using the OS Downloads API
      • Using OS APIs in ESRI Software
    • 🆕OS NGD (National Geographic Database)
      • OS NGD Address
      • OS NGD Boundaries
      • 🆕OS NGD Buildings
        • 🆕Building and Building Access Feature Types
        • Building Part and Building Line Feature Types
      • 🆕OS NGD Geographical Names
      • OS NGD Land
      • OS NGD Land Cover enhancements
      • 🆕OS NGD Land Use
      • OS NGD Land Use enhancements
      • 🆕OS NGD Structures
        • 🆕OS NGD Structures
        • Field Boundaries
      • 🆕OS NGD Transport Features
      • 🆕OS NGD Transport Network
      • OS NGD Transport RAMI
      • OS NGD Water Features
      • OS NGD Water Network
      • OS NGD API - Features
      • Ordering OS NGD data
      • Change only updates
      • OS NGD Versioning
      • Creating a topographic map from OS NGD Data
      • Analytical styling for OS NGD data
    • OS MasterMap® demonstrators
    • 🆕Product & API Comparisons
      • 🆕Comparison of Water Network Products
  • Tutorials
    • GeoDataViz
      • Thematic Mapping Techniques
      • Downloading and using data from the OS Data Hub
      • How to download and use OS stylesheets
      • How to use the OS Maps API
      • Creating a bespoke style in Maputnik
    • GIS
      • Analysing pavement widths
      • Basic routing with OS Open Data and QGIS
      • Walktime analysis using OS Multi-modal Routing Network and QGIS
      • Creating 3D Symbols for GIS Applications
      • Constructing a Single Line Address using a Geographic Address
      • Creating a Digital Terrain Model (DTM)
      • Visualising a road gradient using a Digital Terrain Model
      • Visualising a road gradient using OSMM Highways
    • 🆕APIs
      • 🆕Using OS APIs with EPC API
      • 🆕OS APIs and ArcGIS
  • Deep Dive
    • Introduction to address matching
    • Guide to routing for the Public Sector
      • Part 1: Guide to routing
      • Part 2: Routing software and data options
      • Part 3: Building a routable network
    • Unlocking the Power of Geospatial Data
    • Using Blender for Geospatial Projects
    • A Guide to Coordinate Systems in Great Britain
      • Myths about coordinate systems
      • The shape of the Earth
      • What is position?
        • Types of coordinates
        • We need a datum
        • Position summary
      • Modern GNSS coordinate systems
        • Realising WGS84 with a TRF
        • The WGS84 broadcast TRF
        • The International Terrestrial Reference Frame (ITRF)
        • The International GNSS Service (IGS)
        • European Terrestrial Reference System 1989 (ETRS89)
      • Ordnance Survey coordinate systems
        • ETRS89 realised through OS Net
        • National Grid and the OSGB36 TRF
        • Ordnance Datum Newlyn
        • The future of British mapping coordinate systems
        • The future of British mapping coordinate systems
      • From one coordinate system to another: geodetic transformations
        • What is a geodetic transformation?
        • Helmert datum transformations
        • National Grid Transformation OSTN15 (ETRS89–OSGB36)
        • National Geoid Model OSGM15 (ETRS89-Orthometric height)
        • ETRS89 to and from ITRS
        • Approximate WGS84 to OSGB36/ODN transformation
        • Transformation between OS Net v2001 and v2009 realisations
      • Transverse Mercator map projections
        • The National Grid reference convention
      • Datum, ellipsoid and projection information
      • Converting between 3D Cartesian and ellipsoidal latitude, longitude and height coordinates
      • Converting between grid eastings and northings and ellipsoidal latitude and longitude
      • Helmert transformation worked example
      • Further information
  • Code
    • Ordnance Survey APIs
    • Mapping
    • Routing with pgRouting
      • Getting started with OS MasterMap Highways and pgRouting
      • Getting started with OS MasterMap Highways Network - Paths and pgRouting
      • Getting started with OS NGD Transport Theme and pgRouting
      • Getting started with OS NGD Transport Path features and pgRouting
  • RESOURCES
    • 🆕Data Visualisation External Resources
Powered by GitBook

Website

  • Ordnance Survey

Data

  • OS Data Hub
On this page

Was this helpful?

  1. Deep Dive
  2. A Guide to Coordinate Systems in Great Britain

Datum, ellipsoid and projection information

PreviousThe National Grid reference conventionNextConverting between 3D Cartesian and ellipsoidal latitude, longitude and height coordinates

Last updated 4 months ago

Was this helpful?

Shape and size of biaxial ellipsoids used in the UK

Name
Semi-major axis a (m)
Semi-minor axis b (m)
Associated datums and projections

Airy 1830

6 377 563.396

6 356 256.909[10]

OSGB36, National Grid

Airy 1830 modified

6 377 340.189

6 356 034.447

Ireland 65, Irish National Grid

International 1924 aka Hayford 1909

6 378 388.000

6 356 911.946

ED50, UTM

GRS80 aka WGS84 ellipsoid

6 378 137.000

6 356 752.3141

WGS84, ITRS, ETRS89.

The ellipsoid squared eccentricity constant e² is computed from a and b by equation (B1).

Transverse Mercator projections used in the UK

Projection
Scale factor on central meridian (F₀)
True origin, Φ₀ and λ₀
Map coordinates of true origin (metres), E₀ and N₀
Ellipsoid

National Grid

0.9996012717

lat 49° N

long 2° W

E 400 000

N -100 000

Airy 1830

Irish National Grid

1.000035

lat 53°30′ N

long 8° W

E 200 000

N 250 000

Airy 1830 modified

UTM zone 29

0.9996

lat 0°

long 9° W

E 500 000

N 0

International 1924 or WGS84

UTM zone 30

0.9996

lat 0°

long 3° W

E 500 000

N 0

International 1924 or WGS84

UTM zone 31

0.9996

lat 0°

long 3° E

E 500 000

N 0

International 1924 or WGS84

EPSG codes for common datums and coordinate operations in GB

Many geographic information systems (GIS) and other methods of handling digital geographic data use unique identifiers - Spatial Reference System Identifier (SRID) - for datums, coordinate systems etc.. See . A commonly used SRID Authority is the EPSG (European Petroleum Survey Group) who maintain an online registry of SRIDs at .

EPSG codes of ellipsoids, datums and coordinate operations in common use in the Great Britain.

Datum (and associated coord ref system) or operation name
EPSG SRID code

Airy 1830 ellipsoid

7001

GRS80 ellipsoid

7019

WGS84 ellipsoid

7030

OSGB36 Datum, 2D lat/long

4277

OSGB36 Datum, 2D National Grid

27700

OSGB36 Datum, 3D National Grid + ODN height

7405

ODN Vertical Datum

5701

ETRS89 Datum, 2D lat/long

4258

ETRS89 Datum, 3D lat/long/Height

4937

ETRS89 Datum, 3D XYZ

4936

WGS84 Datum, 2D lat/long

4326

WGS84 Datum, 3D lat/long/Height

4979

WGS84 Datum, 3D XYZ

4978

OSTN15 transformation, native 1km grid

7953

OSTN15 transformation, NTv2 version

7709

OSGM15 transformation, ODN

7711

OSGM15 transformation, Orkney Datum

7712

OSGM15 transformation, “Newlyn offshore”

7713

OSGM15 transformation, Lerwick Datum

7714

OSGM15 transformation, Stornoway Datum

7715

OSGM15 transformation, St. Marys Datum (Scilly Isles)

7716

OSGM15 transformation, Douglas Datum (IoM)

7717

WGS84 < - > OSGB36 Helmert transformation (section 6.6)

1314

ETRS89 lat/long + ODN height compound CRS

9424

ETRS89 lat/long + ODN (Offshore) height compound CRS

9425

ETRS89 lat/long + Orkney height compound CRS

9426

ETRS89 lat/long + Lerwick height compound CRS

9427

ETRS89 lat/long + Stornoway height compound CRS

9428

ETRS89 lat/long + Douglas height compound CRS

9429

ETRS89 lat/long + St. Marys height compound CRS

9430

British Isles height ensemble (approx. MSL height across whole of British Isles)

1288

ETRS89 lat/long + British Isles height ensemble compound CRS

9542

https://en.wikipedia.org/wiki/Spatial_reference_system#Identifier
https://epsg.org/home.html