Coordinate Systems & Datums of Nepal: WGS84, Everest 1830, MUTM & UTM

Nepal does not have a single coordinate system; it has a small family of them, and which one you use depends on whether you are working with global data or official Nepali government data. The two questions that matter are: (1) which datum (the reference model of the Earth's shape and position) your data sits on, and (2) which map projection (the flat grid) it is drawn on. Getting either wrong shifts features by hundreds of metres.

For global, GPS and web-map data, Nepal uses WGS84 (World Geodetic System 1984), catalogued as EPSG:4326 for latitude/longitude and projected onto Universal Transverse Mercator (UTM) zones 44N (EPSG:32644) and 45N (EPSG:32645). For official topographic and cadastral (land-parcel) mapping, the Survey Department of Nepal (Napi Bibhag) uses the Everest 1830 ellipsoid with the Nepal 1981 datum, projected through the Modified UTM (MUTM) system.

The single most common mistake in Nepali GIS is loading Survey Department (MUTM / Everest 1830) data as if it were WGS84 UTM. Because the Everest 1830 and WGS84 ellipsoids differ, and because the datum origins differ, the same ground point can plot roughly 700-900 metres apart between the two systems until a proper datum transformation is applied. Always confirm the datum before you overlay layers.

The table below summarises the four systems you are most likely to encounter for Nepal. Two are geographic (angular latitude/longitude on an ellipsoid) and two families are projected (metres on a flat grid). The projected systems all use a Transverse Mercator projection but differ in their datum, central meridian, zone width and scale factor.

The key distinction is that standard UTM divides the world into 6-degree-wide zones with a scale factor of 0.9996, while Nepal's MUTM uses narrower 3-degree zones with a scale factor of 0.9999, chosen to reduce scale distortion across Nepal's wide east-west extent and to serve high-precision cadastral surveys.

Because a single UTM 6-degree zone cannot cover all of Nepal accurately, standard UTM splits the country at 84 degrees East: everything west uses zone 44N and everything east uses zone 45N. MUTM instead uses three overlapping 3-degree zones centred on 81, 84 and 87 degrees East for tighter accuracy.

WGS84 (World Geodetic System 1984) is the global reference system used by the Global Positioning System (GPS), Google Maps, OpenStreetMap and virtually all satellite imagery. Its geographic form, EPSG:4326, expresses positions as latitude and longitude in decimal degrees on the WGS84 ellipsoid. That ellipsoid has a semi-major axis of 6,378,137 metres and an inverse flattening of 298.257223563, with the Greenwich prime meridian.

EPSG codes come from the EPSG Geodetic Parameter Dataset, an internationally maintained registry of coordinate reference systems. When someone says a dataset is "in EPSG:4326" they mean plain WGS84 latitude/longitude. This is the format you get from a phone GPS, a Google Maps pin, or a GPX track, so it is the natural interchange format for sharing Nepali location data internationally.

WGS84 is a geocentric, satellite-derived datum whose origin is the Earth's centre of mass. This is what makes it globally consistent but also what makes it differ from Nepal's older, locally fitted Everest 1830 datum, which was surveyed to best fit the South Asian region rather than the whole planet.

Long before satellites, the Indian subcontinent was mapped using the Everest 1830 ellipsoid, defined by Sir George Everest during the Great Trigonometrical Survey of India. Nepal's official geodetic datum, Nepal 1981 (EPSG:6207), is built on the Everest 1830 (1937 Adjustment) ellipsoid, which has a semi-major axis of 6,377,276.345 metres and an inverse flattening of 300.8017. Note this ellipsoid is both smaller and differently flattened than WGS84, which is exactly why coordinates do not match between the two without a transformation.

The Nepal 1981 datum is realised through a network of control points and is sometimes referred to by the name of its fundamental reference area, Nagarkot, on the rim of the Kathmandu Valley. Data on this datum is what you find in the Survey Department's topographic map series and in cadastral (land-parcel) records, so it underpins the legal boundaries of land ownership across Nepal.

To move between the Nepal (Everest 1830) datum and WGS84, the Survey Department publishes geocentric translation (Molodensky-type) parameters. A commonly cited set of three-parameter shifts is approximately dX = +293.17 m, dY = +726.18 m, dZ = +245.36 m (Everest 1830 to WGS84). These values are indicative national averages; higher-accuracy work uses region-specific (eastern and western Nepal) parameter sets published by the Survey Department, so always use the parameters appropriate to your area and required precision.

The Modified Universal Transverse Mercator (MUTM) is the projection the Survey Department adopted for official Nepali mapping. It is a Transverse Mercator (Gauss-Kruger) projection, but modified from standard UTM in two important ways to suit Nepal's geography and cadastral accuracy needs. First, it uses 3-degree-wide zones instead of UTM's 6-degree zones. Second, it uses a scale factor of 0.9999 at the central meridian instead of UTM's 0.9996, which further reduces distortion within each zone.

MUTM covers Nepal with three zones identified by their central meridians: zone 81 (central meridian 81 degrees E) for western Nepal, zone 84 (84 degrees E) for central Nepal, and zone 87 (87 degrees E) for eastern Nepal. Like UTM, each zone applies a false easting of 500,000 metres so that all easting values stay positive, a false northing of 0 metres, and a latitude of origin at the Equator (0 degrees). The ESRI-catalogued form of this system is Nepal Nagarkot TM (ESRI:102306), using the Nepal 1981 datum.

The practical payoff of MUTM's narrower zones and higher scale factor is smaller linear distortion across Nepal's roughly 800-kilometre east-west span, which matters for precise cadastral and engineering surveys. The trade-off is that MUTM is a Nepal-specific system: to share MUTM data with international tools or overlay it on satellite imagery, you must first reproject it to a WGS84-based system such as UTM 44N/45N or geographic EPSG:4326.

When you need Nepal data in a globally interoperable projected grid (for example to combine it with Sentinel or Landsat imagery, or to run analysis in a mainstream GIS), the standard choice is WGS84 UTM. Nepal falls across two UTM zones. Zone 44N (EPSG:32644) covers the western part of the country, west of 84 degrees E, with a central meridian of 81 degrees E. Zone 45N (EPSG:32645) covers the eastern part, east of 84 degrees E, with a central meridian of 87 degrees E.

Both zones share the standard UTM parameters: a Transverse Mercator projection on the WGS84 ellipsoid, a scale factor of 0.9996 at the central meridian, a false easting of 500,000 metres, a false northing of 0 metres (northern hemisphere), a latitude of origin at the Equator, and coordinates in metres. Because the datum is WGS84, these grids line up correctly with GPS and satellite data without any datum shift.

A useful memory aid: UTM 44N and MUTM zone 81 share the same 81-degree central meridian, and UTM 45N and MUTM zone 87 share the same 87-degree central meridian. But they are not interchangeable, because UTM uses WGS84 with a 0.9996 scale factor while MUTM uses Everest 1830 / Nepal 1981 with a 0.9999 scale factor. The coordinates will differ even where the meridians match.

These three parameters appear in every projected system above, so it helps to understand what they do. The scale factor at the central meridian is a deliberate shrink applied down the middle of a zone so that distortion is balanced (slightly too small in the centre, slightly too large at the edges) rather than piling up at one side. UTM's 0.9996 and MUTM's 0.9999 are both less than 1 for this reason; MUTM's value is closer to 1 because its narrower 3-degree zones need less correction.

False easting is a constant added to every easting value so that no coordinate is negative. All of Nepal's projected systems add 500,000 metres of false easting, meaning the central meridian of each zone is labelled 500,000 m E, with points to the west having smaller values and points to the east larger. False northing is a constant added to northings; for the northern hemisphere (all of Nepal), it is 0 metres, so northings are simply the distance in metres north of the Equator.

Understanding these values also explains a frequent confusion: a large easting like 340,000 or 660,000 does not mean a location is far from Nepal; it just reflects the 500,000-metre offset from the zone's central meridian. If you ever see coordinates near 500,000 easting and a few million northing in metres, you are almost certainly looking at a UTM or MUTM grid rather than latitude/longitude.