Coordinate Format Cheatsheet

Eight coordinate formats account for nearly every real-world use of geographic coordinates: decimal degrees, degrees-minutes-seconds, degrees-decimal-minutes, UTM, MGRS, Plus codes, geohash, and Maidenhead grid locators. They are not interchangeable — each has a defined precision granularity, a regional or domain bias, and a primary specification that governs its syntax. This page gives the Empire State Building (40.7484° N, 73.9857° W) in every format, with the canonical spec and the practical use case for each.

At a glance

Each row below contains the same point, encoded eight different ways.

Precision per digit

Every format has a granularity that scales with its character count. The table below gives the linear distance corresponding to a one-character change at mid-latitudes (approximately the Empire State Building's latitude). All values are at the Earth's surface.

Per-format details

Decimal Degrees (DD)

The canonical numerical form. Latitude is a signed real number in [−90, 90]; longitude in [−180, 180]. Negative latitude is south, negative longitude is west. The order in ISO 6709 is latitude first, then longitude. Six fractional digits gives roughly 11 cm of resolution at the equator and somewhat less at higher latitudes due to longitudinal compression.

Use when: storing in a database, calling a web geocoding API, doing distance calculations. This is the machine-to-machine default.

Avoid when: speaking aloud or recording by hand — the trailing decimals are error-prone without visual anchors.

Degrees, Minutes, Seconds (DMS)

The traditional sexagesimal form, used on every nautical chart and aviation chart published in the twentieth century. One degree = 60 arc minutes; one arc minute = 60 arc seconds. One arc minute of latitude equals one nautical mile (1852 m) by definition — that history is why DMS persists in marine and aeronautical contexts.

Use when: working with legacy charts, court records, or any document that already uses DMS — converting introduces rounding error.

Avoid when: doing arithmetic. Always convert to decimal degrees before calculation.

Degrees, Decimal Minutes (DDM)

Hybrid form: degrees and minutes are integer/decimal as in DMS, but seconds are absorbed into the minutes field as a decimal fraction. This is the format emitted by every GPS receiver that speaks NMEA 0183, the marine and aviation GPS protocol since the early 1980s.

Use when: integrating with marine GPS, reading NMEA sentences, or following navigation manuals from the 1980s onward.

Avoid when: contexts that expect strict DMS or decimal degrees — there is no automatic conversion from DDM in many GIS tools.

UTM (Universal Transverse Mercator)

UTM divides Earth into 60 longitudinal zones of 6° each. Within a zone, a position is given as (zone, hemisphere, easting, northing) in metres. Easting is metres east of the false origin (500 000 m); northing is metres north of either the equator (N hemisphere) or the south pole at 10 000 000 m (S hemisphere). The zone's central meridian is the line of zero distortion; distortion grows to about 1 part in 1000 at the zone edges.

Use when: doing surveying, civil engineering, or ground-distance calculations within a single zone — UTM is the only metric, locally accurate, zone-relative grid widely published.

Avoid when: working across zone boundaries (zones are not joined seamlessly), or in polar regions — Universal Polar Stereographic (UPS) covers above 84° N or below 80° S instead.

MGRS (Military Grid Reference System)

A NATO standard that wraps UTM coordinates in a compact alphanumeric form. Format: [zone][latitude band] [100 km square ID] [easting] [northing]. The 100 km square ID is two letters that uniquely identify a 100 × 100 km cell within the zone. The easting and northing are then expressed in 1 to 5 digit pairs for 10 km, 1 km, 100 m, 10 m, or 1 m resolution.

Use when: military operations, NATO joint operations, search-and-rescue, or any context that follows the DoD or Allied joint geospatial standards.

Avoid when: civilian web applications and general public communication — Plus codes or DD are vastly more legible.

Plus Codes (Open Location Code)

Google's open specification for a short, addressable code derived from a base-20 encoding of latitude and longitude. Full codes are 10 or 11 characters (with a + separator after the first eight). They can be shortened by appending a locality (e.g. P2X7+9P New York) to drop the leading prefix.

Use when: communicating a location to someone who has Google Maps but no street address — rural homes, informal settlements, points in open space, meeting spots in parks.

Avoid when: legal records, cadastral surveys, or contexts that need a numeric coordinate.

Geohash

A 2008 invention by Gustavo Niemeyer: encode latitude and longitude into a single string by interleaving the binary expansions of each, then base-32 encode the result. Each appended character refines both axes by a factor of √32 ≈ 5.66 in linear resolution.

Use when: spatial indexing in a database (proximity queries on a single string column), bucketing coordinates into discrete cells, deduplicating clustered points.

Avoid when: human reading, navigation, publishing — geohash cells do not align with administrative boundaries and can cross the antimeridian or poles ungracefully.

Maidenhead Grid Locator

Amateur radio's coordinate format. Designed at the IARU Region 1 conference in Maidenhead, UK in 1980 (Karl Hille, DL1VU). Four-character codes denote a 2° × 1° rectangle (called a grid square); six characters refine to a subsquare; eight characters to an extended subsquare.

Use when: HF/VHF/UHF radio logs, grid hunting, contest exchanges — anywhere the IARU or ARRL grid square is the lingua franca.

Avoid when: any non-amateur-radio context. Maidenhead has unusual symmetries (each field is 20° of longitude but only 10° of latitude) that make it counter-intuitive for general spatial work.

How to choose

A short decision tree:

• Storing or computing on coordinates? → DD.
• Reading from a legacy chart, court record, or aviation publication? → DMS.
• Reading a marine GPS or NMEA sentence? → DDM.
• Doing land surveying or engineering inside one country/zone? → UTM.
• Coordinating with military or SAR teams? → MGRS.
• Sharing a location without a street address? → Plus code.
• Building a spatial index in a key-value store? → geohash.
• Logging an amateur radio contact? → Maidenhead.

When in doubt, store as DD in the database, present in whichever format the user expects, and convert between them with the Coordinate Converter.