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Geodesy

WGS 84: World Geodetic System 1984

Updated · GeoCAD Bridge engineering team · 8 min read

Summary

WGS 84 is the global geodetic reference system used by GPS. It defines an ellipsoid (a = 6 378 137 m, 1/f = 298.257223563) and a reference frame that has been realized several times (G730 to G2296), each aligned to the ITRF at centimetre level. Because EPSG treats WGS 84 as a datum ensemble, “WGS 84” on its own carries an uncertainty of about 2 m; precise work should name the realization or use a modern national frame.

Definition

WGS 84: the World Geodetic System 1984, an Earth-centred, Earth-fixed reference system with its own ellipsoid, maintained by the US NGA.

  • a = 6 378 137 m
  • 1/f = 298.257223563
  • Geographic 2D: EPSG:4326
  • Geographic 3D: EPSG:4979
  • Ensemble accuracy ≈ 2 m
  • Latest: WGS 84 (G2296)

Ellipsoid and frame

The WGS 84 ellipsoid is almost identical to GRS 80; the semi-minor axes differ by about 0.1 mm. The reference frame is Earth-centred and realized by the coordinates of GPS tracking stations. Successive realizations G730 (1994), G873, G1150, G1674, G1762, G2139 and G2296 (2024) have brought it into agreement with the International Terrestrial Reference Frame (ITRF) at the centimetre level.

EPSG codes

Common WGS 84 based CRSs.
EPSGTypeAxes
4326Geographic 2DLatitude, longitude (degrees)
4979Geographic 3DLatitude, longitude, ellipsoidal height
4978GeocentricX, Y, Z (metres)
3857Projected (Pseudo-Mercator)Easting, northing
32601–32660 / 32701–32760Projected (UTM)Easting, northing

WGS 84 versus national frames

Plates move. Saudi Arabia moves about 3 cm per year in ITRF, so coordinates tied to a fixed epoch drift away from current WGS 84 coordinates over time. National frames such as KSA-GRF17, ETRS89 and GDA2020 are fixed to their plate, so survey marks keep stable coordinates. EPSG’s default KSA-GRF17 to WGS 84 transformation is effectively a null transformation with 1 m accuracy, reflecting the WGS 84 ensemble uncertainty rather than the true difference at any epoch.

Common mistakes

  • Assuming WGS 84 coordinates from different years are identical at centimetre level.
  • Confusing EPSG:4326 axis order (latitude first) with GeoJSON order (longitude first); see axis order.
  • Calling Web Mercator “WGS 84”.

FAQ

Is WGS 84 the same as GPS coordinates?

GPS broadcast orbits are expressed in WGS 84, so a stand-alone GPS position is in WGS 84 with metre-level accuracy.

Is WGS 84 the same as ITRF?

Recent WGS 84 realizations agree with the corresponding ITRF at about 1–2 cm, so they are often treated as equal for mapping, but they are maintained separately.

What is the difference between WGS 84 and GRS 80?

The ellipsoids differ only in flattening at the 10⁻¹¹ level, about 0.1 mm in the semi-minor axis. The reference frames that use them can differ by much more.

What does EPSG:4326 mean?

It is the EPSG code for the WGS 84 geographic 2D CRS with latitude and longitude in degrees.

Tools

Articles

References

  1. NGA. World Geodetic System 1984: Its Definition and Relationships with Local Geodetic Systems, NGA.STND.0036.
  2. IOGP. EPSG Geodetic Parameter Dataset, epsg.org.
  3. IERS. International Terrestrial Reference Frame, itrf.ign.fr.

Cite this page

GeoCAD Bridge. “WGS 84: World Geodetic System 1984.” GeoCAD Bridge Knowledge Center, updated 2026-10-05. https://www.geocadbridge.com/knowledge/coordinate-systems-wgs84/