WGS84 Datum: The Reference Frame Behind GPS in India

What is WGS84?

WGS84 is a geodetic datum and reference frame maintained by the United States for the Global Positioning System (GPS). It defines the Earth's centre, the orientation of the axes and an ellipsoid that approximates the Earth's shape. Every position a GPS receiver computes is first expressed in WGS84; the familiar code EPSG:4326 means WGS84 latitude and longitude.

Coordinates we deliver state this datum. If the same plot also needs scanning for cables, see your price in seconds.

The frame has been refined several times using ground-based reference stations around the world, and recent versions agree with the International Terrestrial Reference Frame at the centimetre level. Because the Indian plate drifts roughly 5 cm a year to the north-east, the date of a centimetre-level coordinate matters on long-lived projects.

How does WGS84 differ from older Indian datums?

Older Survey of India mapping used the Everest ellipsoid with the Indian datum, whose origin is at Kalianpur in Madhya Pradesh. The two systems differ by tens of metres or more on the ground. A boundary digitised from an old sheet and laid over WGS84 data can land in the wrong field. Open Series Maps since 2005 use WGS84, which removes the problem for new work but not for old drawings.

Why are GPS heights different from levels?

A receiver measures height above the WGS84 ellipsoid (h); drawings normally need height above mean sea level (H), which follows the geoid. The gap between them, the geoid separation N, is tens of metres across India, and the geoid lies below the ellipsoid over most of the country. A geoid model converts one to the other, but for drainage-grade accuracy we still check against a levelled benchmark.

How many decimal places does a coordinate need?

At least six for metre-level mapping and seven for survey work. One degree of latitude is about 111 km, so the fourth decimal place of a degree is about 11 m. The fifth is about 1.1 m, the sixth about 11 cm and the seventh about 1 cm. A plot corner quoted as 28.4089, 77.3178 is therefore only good to a few metres, however carefully it was measured. Mezux coordinate files give WGS84 latitude and longitude to at least seven decimal places alongside the UTM values.

A worked example of drift with time

A fixed pillar's WGS84 coordinates change slowly because the plate moves under the frame. At roughly 5 cm a year, a pillar coordinated in 2016 will read about 50 cm away by 2026 in an Earth-fixed frame. Yet it has not moved relative to the ground around it. For mapping that hardly matters. For a ten-year infrastructure project tied to centimetre control it does, which is why survey reports state the epoch of the coordinates as well as the frame. Reference station coordinates are published for a stated epoch for the same reason, and a base station fixed years earlier needs that note too.

Heights need the same care. If a geoid model gives a separation of −45 m at a site, an ellipsoidal height of 160 m corresponds to roughly 205 m above mean sea level. The sign of that separation is a frequent source of 90 m blunders.

Common WGS84 mix-ups

Small formatting slips cause most WGS84 errors, and they can shift a point by metres or more.

• Typing degrees-minutes-seconds into a field that expects decimal degrees.
• Overlaying a drawing digitised from an Everest-based sheet on WGS84 imagery without transformation.
• Reading KML altitude as height above sea level when the file says it is relative to the ground.

WGS84 itself is maintained by the US National Geospatial-Intelligence Agency, and ISO 19111 sets the general rules for describing such reference systems.

Where WGS84 appears in Mezux deliverables

On every coordinate file, KMZ and drawing title block. Latitude and longitude in our files are WGS84 to at least seven decimal places, and projected values are WGS84 UTM in the stated zone. Heights are marked either as ellipsoidal or as reduced levels above mean sea level, never left ambiguous. When a client sends an older drawing on another datum, we state the transformation applied and its expected accuracy before overlaying our work on it.

WGS84 on land and utility jobs

It is the common language of satellite-based positioning, linking field crews, Google Earth and GIS. When a Haryana plot is set out from its revenue papers, the corners we fix are delivered in WGS84 and UTM so the owner can see them on a map. That is where DGPS works best for land owners. How the parcel is identified is explained in Khasra and Killa Numbers, and who owns it in Jamabandi (Haryana Land Record). KMZ files are always WGS84.

See the questions to ask before a total station survey, or book a survey slot for your project.

Frequently asked questions

Is WGS84 a projection?

No. It is a datum and coordinate frame. Projections such as UTM are built on top of it to give flat grid coordinates.

Does Google Earth use WGS84?

Yes. KML and KMZ coordinates are WGS84 latitude, longitude and height.

What coordinate files do I get from a DGPS survey?

Excel or CSV, DWG and KMZ, all stating the datum. A differential global positioning system (DGPS) survey removes most GPS error but still reports in WGS84. See what you receive from a DGPS survey.

Is WGS84 the same as ITRF?

Recent realisations agree with the International Terrestrial Reference Frame at the centimetre level, so for most work they are treated as the same, but they are defined separately.

Why does my old drawing not line up with Google Earth?

It may be on an older Indian datum or a local grid. Without the right transformation it can sit tens of metres away.

Should heights in a WGS84 file be trusted for drainage?

Not on their own. They are ellipsoidal; they need a geoid model and a check against a levelled benchmark.

Does a phone's map app use WGS84?

Yes. Phones compute positions from GPS signals in WGS84, and most web maps report WGS84 latitude and longitude, though their accuracy is metres, not centimetres.

Which EPSG code should a KMZ use?

None needs choosing: KML and KMZ are defined in WGS84 longitude and latitude, equivalent to EPSG:4326, so software assumes it automatically.

Written by Saniya Parveen · Technically reviewed by Rahul Rai · Updated 8 November 2026