Coordinate Formats Explained

A geographic coordinate can be written eight common ways: decimal degrees (DD), degrees-minutes-seconds (DMS), degrees-decimal-minutes (DDM), UTM, MGRS, Plus Codes, geohash, and Maidenhead. All eight describe the same point on the WGS-84 ellipsoid; the format is a domain choice, not an information choice.

A coordinate format is just a way of writing the same two angles. The Empire State Building's position on the WGS-84 ellipsoid can be written as 40.7484, -73.9857, as 40°44′54.24″N 73°59′08.52″W, as 40°44.904′N 73°59.142′W, as 18T 585628 mE 4511322 mN, as 18TWL 85628 11322, or as 87G8P2X7+9P — six distinct rows for one identical point. This article defines each, runs the Empire State Building through all of them, gives a master comparison table, and addresses the misconceptions that conflate precision with accuracy or format with datum.

Why multiple formats exist

There is no single “right” coordinate format. Decimal degrees are the mathematically simplest representation but harder to read aloud. DMS preserves the base-60 arithmetic that astronomers and surveyors have used since Babylon. DDM compromises the two for the navigator who wants to read “minutes” off a sextant. UTM and MGRS were designed for ground operations in metres rather than degrees; Plus Codes were designed by Google for places without street addresses.

The international standard for the angular representations is ISO 6709:2022, which allows DD, DMS, and DDM as equivalent with latitude first. UTM and MGRS are governed by NGA TM 8358.1 and the underlying transverse-Mercator math is in USGS Professional Paper 1395. Plus Codes have their own open specification published by Google; geohash and Maidenhead are public-domain conventions outside ISO.

Decimal degrees (DD)

Decimal degrees express each coordinate as a single signed decimal number, latitude first per ISO 6709. The Empire State Building is 40.7484, -73.9857 — or 40.7484°N, 73.9857°W if hemisphere letters are used instead of signs.

Civilian GPS resolves about 4.9 m (95%) under open sky per GPS.gov, which makes the fifth decimal place the practical floor on smartphone-derived DD. Sixth-decimal precision is honest only for differential or RTK GPS, surveyed control points or cadastral data. Longitude resolution at the same decimal count shrinks with latitude — six decimals at the equator is 11 cm, but at 60° latitude it is 5.5 cm because 1° of longitude is only 55.8 km there.

Degrees, minutes, seconds (DMS)

Degrees-minutes-seconds inherits Babylon's base-60 arithmetic — the same convention that gives the world 60 minutes in an hour and 60 seconds in a minute. ISO 6709 allows DMS as one of the three canonical angular representations. The Empire State Building in DMS is 40° 44′ 54.24″ N, 73° 59′ 08.52″ W.

The conversion from DD to DMS is mechanical: the degrees are the integer part, the fractional part times 60 gives total arcminutes, the integer part of that is the minutes, and the remaining fractional part times 60 gives the arcseconds.

DMS is the convention on paper topographic maps (USGS quadrangles, Ordnance Survey Explorer maps, IGN maps in France), in surveying field notes, and in older navigation publications. A typographic note: the arcminute mark is a prime (Unicode ′); the arcsecond mark is a double prime (Unicode ″). ASCII apostrophe and quote are universal fallbacks; curly typographic quotes (“ ”) are incorrect, though autocorrect often introduces them.

Degrees, decimal minutes (DDM)

DDM splits the difference between DD and DMS. The degrees are an integer; the arcminutes carry the decimal. The Empire State Building in DDM is 40° 44.904′ N, 73° 59.142′ W.

DDM is the marine and aviation choice. The reason is the historical identity 1 arcminute of latitude = 1 nautical mile — reading “44.904 minutes” off a sextant tells a navigator how far north of the previous reference line they are, in nautical miles, with no further arithmetic. Garmin GPSMAP marine receivers, ICAO-compliant flight planning systems and the AIS maritime tracking infrastructure all default to DDM.

Universal Transverse Mercator (UTM)

UTM is a projected grid system, not a geographic coordinate — it divides Earth's surface into 60 longitudinal zones, each 6° wide, and projects each zone separately onto a plane using the transverse Mercator projection per Snyder 1987. Within a zone, positions are given as easting and northing in metres from a synthetic origin.

The Empire State Building in UTM is 18T 585628 mE 4511322 mN.

The 0.9996 central-meridian scale factor compresses the central meridian by 0.04% so that the maximum distortion at the zone edges (where distortion peaks) is roughly equal in magnitude to the central-meridian compression — an old surveyor's trick that keeps the total error budget within a zone close to 1 part in 2,500. Zones 31V, 32V, 31X, 33X, 35X and 37X are the published exceptions, widened or shifted to keep southern Norway and Svalbard in single zones.

Military Grid Reference System (MGRS)

MGRS is UTM with a more compact, voice-friendly notation. Where UTM spells out the easting and northing in metres, MGRS prefixes a two-letter identifier for the 100-km grid square within a zone, then truncates the easting and northing to within that square.

The Empire State Building in MGRS is 18T WL 85628 11322.

The military designed MGRS for grid-reference communication over a radio: 18T WL 8562 1132 is shorter to speak than 18T 585628 4511322, and the digit count tells the listener the precision immediately. MGRS is the operational default for US and NATO forces, US Search and Rescue, and many other ground-operations systems. Polar regions use a separate UPS extension, out of scope for this article.

Plus Codes (Open Location Code)

Plus Codes are Google's open-source compact location encoding, designed to address places that lack street addresses — rural areas, informal settlements, fields, beaches. The full open specification is published with reference implementations in 10+ languages.

The Empire State Building in Plus Codes is 87G8P2X7+9P.

Plus Codes have three useful properties for sharing. They are locally compact — nearby places share a prefix, so 87G8P2X7+9P and 87G8P2X7+9Q are adjacent. They support a short-code form — the full 11-character global code can be abbreviated to P2X7+9P, New York when a reference city is named, dropping the high-order region characters. And the open specification means any software can encode or decode without licensing fees.

Side-by-side comparison

All six rows describe the same physical point on WGS-84. The DMS ↔ decimal converter handles the three angular notations, /tools/utm-converter handles UTM, /tools/mgrs-converter handles MGRS, and /tools/plus-codes handles Plus Codes.

Briefly: geohash and Maidenhead

Two more alphanumeric formats appear often enough to mention. They are specialist tools rather than general-purpose coordinates, but they share the “short string encodes a location” property with Plus Codes.

Geohash interleaves latitude and longitude bits before encoding into base-32 — this means nearby places usually share a prefix, but the mapping is irregular near the antimeridian and the equator. Maidenhead divides the world into 18° × 9° “fields,” then 1° × 2° squares, then finer subdivisions; amateur radio operators use it to report rough station location. The /reference/coordinate-format-cheatsheet covers both in full detail.

Common misconceptions

Related pillars

The other seven pillar concepts on Coordinately:

• What is latitude and longitude? — the angular coordinates every format encodes
• How GPS works — the system that produces the values you format
• What is a map projection? — the math behind UTM and MGRS
• What is a geodetic datum? — what every format silently references
• Time zones explained — how longitude maps to civil time
• History of latitude and longitude — where the formats came from
• Great-circle distance — using formatted coordinates to compute distance