Coordinately

How to Read Coordinates

A practical guide to decoding a coordinate when you see one — identify the format (DD, DMS, DDM, UTM, MGRS, Plus Code), decode each component, recognise the precision, and avoid the common reading mistakes.

By . Published . Last updated .

A coordinate is a short string of characters that encodes a location. The encoding is straightforward once you know which format you're reading, but the formats look different enough that an unfamiliar one can stop you cold without practice. This article gives a visual identifier for each of the six common formats Coordinately covers, then walks through decoding each component — integer degree, fractional part, hemisphere indicator, and the implicit datum. The companion guide on the inverse direction — producing well-formed coordinates yourself — lives at /learn/how-to-write-coordinates. The pillar that defines what coordinates are in the first place is at /learn/coordinate-formats-explained.

Recognise the format from its visual fingerprint

Each of the six common formats has identifying marks:

Decimal degrees (DD). Two signed decimal numbers separated by a comma or space, often inside parentheses. Example: 40.7484, -73.9857 or (40.7484, -73.9857). Telltales: signed numbers (positive or negative); decimal point; no degree symbol; no quote marks; no zone-band prefix.

Degrees, minutes, seconds (DMS). A degree symbol (°), then a minute marker (') or prime (′), then a second marker (") or double-prime (″), then a hemisphere letter. Example: 40°44'54.24"N, 73°59'08.52"W. Telltales: three numerical components per axis; the symbols ° ' " (or Unicode primes); hemisphere letters N/S/E/W.

Degrees, decimal minutes (DDM). A degree symbol, then a single decimal minute, then a hemisphere letter. Example: 40°44.904'N, 73°59.142'W. Telltales: TWO numerical components per axis (integer degrees + decimal arcminutes, no seconds); degree and minute markers; hemisphere letter.

UTM. A zone number (1–60), a band letter, then two large numbers (easting and northing) in metres. Example: 18T 585628 4511322. Telltales: two-character prefix combining digits and a letter; two large numbers (typically 6–7 digits each); no hemisphere letter on the coordinates themselves; no degree symbol.

MGRS. A UTM zone + band, then a two-letter 100-km square identifier, then digit pairs of varying length. Example: 18TWL8562811322 or with optional spacing 18T WL 85628 11322. Telltales: digits-then-letter prefix; two more letters after; an even number of digits; no degree symbol; no spaces required between groups.

Latitude and longitude axesA rectangular grid showing latitude (horizontal lines) and longitude (vertical lines). The equator runs across the centre, the prime meridian runs down the centre. A sample point at 40.75 degrees north, 73.99 degrees west is marked with crosshairs.60°N30°N30°S60°S120°W60°W60°E120°EEquatorPrime meridian40.75°N, 73.99°WLongitude →Latitude →
The geographic coordinate system every format encodes.— Latitude (horizontal lines) and longitude (vertical lines) are the underlying angular measurements; each format is a different encoding of the same two numbers.

Plus Code (Open Location Code). 8 alphanumeric characters, a + separator, then 2–7 more characters. Example: 87G8P2X7+9P. Telltales: the + character; alphabet drawn from 23456789CFGHJMPQRVWX only (uppercase, no 0/1, no A/B/D/E/I/K/L/N/O, no lowercase).

When the format is ambiguous from a fragment, context resolves it. A comma between two signed decimal numbers almost always means DD; the presence of any degree symbol means DMS or DDM; a + in a single token means a Plus Code; a 1-2 digit zone followed by a letter means UTM or MGRS.

Decode the components

Every coordinate has the same three pieces of information: which side of the equator (latitude sign), which side of the prime meridian (longitude sign), and the angular or grid magnitude in some representation. The decoding rules for each format:

Integer-degree part. The integer before the decimal point (for DD), or the first integer (for DMS / DDM). Latitude is bounded to 0–90 in magnitude; longitude to 0–180.

Fractional part.

  • DD: decimal places after the integer degree. Each decimal place is a factor of 10 in precision.
  • DMS: arcminutes (0 to 59) and arcseconds (0 to 59 plus decimals). Each arcminute is 1/60 of a degree; each arcsecond is 1/3600.
  • DDM: decimal arcminutes (0 to less than 60.000…).
  • UTM: directly in metres of easting and northing within a zone.
  • MGRS: digit pairs giving easting and northing within a 100-km square, again in metres.
  • Plus Code: base-20 alphanumeric encoding; refinement increases with string length.

Hemisphere indicator.

  • DD: the sign of the number. Positive latitude = N; positive longitude = E. Negative = S or W.
  • DMS / DDM: the suffix letter (N, S, E, W).
  • UTM: the band letter indirectly encodes hemisphere. Bands N–X are northern; bands C–M are southern (the letters I and O are skipped to avoid confusion with 1 and 0).
  • MGRS: same as UTM, via the band letter.
  • Plus Code: the first two characters of the code encode the global position to within an 18° × 18° cell.

Precision. The honesty of the coordinate.

  • DD: decimal places. 6 dp ≈ 11 cm at the equator. 3 dp ≈ 111 m. Longitude precision shrinks with latitude.
  • DMS: arcsecond decimals. 0.01" ≈ 31 cm at the equator.
  • DDM: arcminute decimals. 0.001' ≈ 1.85 m at the equator.
  • UTM: 1 m precision is the convention (integer metres).
  • MGRS: digit count tells precision. 10 digits = 1 m; 8 digits = 10 m; 6 = 100 m; 4 = 1 km; 2 = 10 km.
  • Plus Code: code length. 10 characters (default) describes a ~14 m cell; 11 characters ~3 m; 12+ characters sub-metre.

A coordinate with high precision (many decimal places) is not the same as a coordinate with high accuracy. A 7-decimal-place smartphone GPS reading is precise to centimetres but accurate to about 5 m — the trailing digits are computational artifacts. The full distinction lives in /learn/precision-vs-accuracy-in-coordinates (when shipped).

Identify the implicit datum

Most modern coordinates are referenced to the WGS84 datum. When the source doesn't say:

  • GPS readings: WGS84
  • Google Maps, Apple Maps, Mapbox, OpenStreetMap: WGS84
  • Modern surveying datasets in the US: WGS84 or NAD83 (the two are within a few metres of each other for everyday work; surveyors distinguish them carefully, casual users do not)
  • Paper topographic maps published since the 1990s: usually WGS84 or a regionally-aligned equivalent

When a coordinate IS in a different datum, the source typically says so. Common non-WGS84 datums:

  • NAD27 (US, mostly retired) — older paper USGS quad sheets
  • NAD83 (US, transitioning to NATRF2022 through 2027 per NGS)
  • OSGB36 (UK) — used with the British National Grid
  • Tokyo Datum (Japan, mostly retired in favour of JGD2011)
  • ETRS89 (Europe) — used by IGN France, by most EU national grids

The difference between datums is typically tens to hundreds of metres at any given point — invisible on a city map but significant for surveying, legal-boundary work, or aviation.

Common gotchas

Sign and hemisphere letter contradicting each other. A coordinate like +73.9857°W is contradictory: the positive sign claims east; the W claims west. One needs to win, and conventionally the explicit letter takes precedence over the sign. Better: don't produce such coordinates in the first place. Pick one convention per data source.

Latitude and longitude flipped. A coordinate pair like (73.9857, -40.7484) is wrong-order: 73.9857 is in the latitude slot but is in fact a longitude magnitude (so the magnitude is plausible-but-suspicious). A diagnostic test: latitude is bounded to ±90, so any “latitude” greater than 90 in magnitude is definitely a flipped pair (this catches longitudes > 90 in the lat slot). The pillar /learn/why-latitude-comes-first (when shipped) covers the ordering conventions.

Smart quotes. 40°44'54.24"N (curly typographic quotes: ‘ ’ “ ”) versus 40°44'54.24"N (straight ASCII quotes: ' "). Curly quotes come from word processors that auto-correct. Some coordinate parsers reject them; many accept them. Producers should prefer straight ASCII quotes or proper Unicode primes (′ ″) for maximum compatibility.

Missing hemisphere indicator. 40.7484, 73.9857 without sign or letter is ambiguous — it could be (40°N, 73°E), (40°N, 73°W), (40°S, 73°E), or (40°S, 73°W). All four are real points on Earth in different parts of the world. Defensive parsing should reject the unmarked form; careful publishers should always include sign or letter.

DDM mistaken for DMS. 40°44.904'N looks at first glance like 40 degrees, 44 minutes, 904 seconds — but 904 seconds is impossible (arcseconds max out at 59.99…). The format is actually degrees-decimal-minutes: 40 degrees and 44.904 minutes (which equals 44 minutes 54.24 seconds in DMS). The presence of a decimal point inside the minutes value is the telltale.

Worked examples

1. Empire State Building in DD: 40.7484, -73.9857

  • Latitude 40.7484 — positive, so north of the equator
  • Longitude -73.9857 — negative, so west of the prime meridian
  • 4 decimal places per coordinate → ~11 m precision at this latitude
  • Implicit WGS84 (no datum stated; modern context implies WGS84)
  • Decoded as: 40.7484°N, 73.9857°W

2. Eiffel Tower in DMS: 48°51'30.24"N, 2°17'40.20"E

  • Latitude 48° degrees, 51' arcminutes, 30.24" arcseconds, N hemisphere
  • Longitude 2° degrees, 17' arcminutes, 40.20" arcseconds, E hemisphere
  • Arcsecond decimals at 0.01" → about 30 cm precision at the equator
  • Implicit WGS84
  • Decoded as 48.8584°N, 2.2945°E (the same point in DD)

3. Aviation waypoint in DDM: 40°44.904'N, 73°59.142'W

  • Latitude 40° degrees, 44.904' decimal arcminutes, N
  • Longitude 73° degrees, 59.142' decimal arcminutes, W
  • Arcminute decimals at 0.001 → about 1.85 m precision at the equator
  • FAA aviation context — WGS84 is the FAA navigation-database default
  • Decoded as the same Empire State point in DDM (40.7484°N, 73.9857°W)

4. Military grid reference in MGRS: 18T WL 85628 11322

  • Zone 18, band T — eastern US, mid-latitude
  • WL — the 100-km grid square within zone 18T
  • 85628 — easting metres within the square
  • 11322 — northing metres within the square
  • 5+5 digits → 1 m precision
  • The same Empire State point, encoded in MGRS

5. Plus Code: 87G8P2X7+9P

  • 87G8 — the global region (an 18° × 18° cell, then a 1° × 1° cell)
  • P2X7 — the local cells refining to about 14 m × 14 m
  • +9P — two characters of grid refinement narrowing to about 3 m × 3 m
  • The same Empire State point, in Plus Code form

Common misconceptions

Format does not determine accuracy. A 6-decimal DD coordinate is precise to 11 cm, but only as accurate as the source measurement allows. A smartphone-recorded 40.748417, -73.985706 is precise to centimetres but accurate to roughly 5 m — the 5th and 6th decimal places are real, the 7th is decoration. The deep treatment lives in /learn/precision-vs-accuracy-in-coordinates (when shipped).

Hemisphere letters and signed numbers are equivalent, but mixing them in one dataset is a bug. Pick one convention per data source and document it. Mixing produces records like 40.7484, -73.9857°W (positive latitude with a redundant sign-and-letter on longitude) that parsers handle inconsistently.

UTM is not a "better" format than DD — it is a different format for a different use. UTM is for grid-reference work where metric distances within a zone matter. DD is for general computation and storage. Neither is inherently more accurate; both encode the same underlying lat/lon to the precision you specify.

Plus Codes are not encrypted or hashed. They are a regular alphanumeric encoding of latitude and longitude using a 20-character alphabet, with the encoding rule publicly documented. Any Plus Code can be decoded back to coordinates by applying the rule — no key, no external lookup table.

A coordinate without a stated datum is not "datum-free". It has an implicit datum, which is almost always WGS84 in modern contexts. The datum determines what the angular values mean physically; without a datum, the numbers are uninterpretable. Treat unstated coordinates as WGS84 by default and document the assumption.

Related

Frequently asked questions

A coordinate has no hemisphere indicator and no sign. Which hemisphere is it in?

Ambiguous. Without an explicit sign or hemisphere letter, '40.7484, 73.9857' could mean (40.7484°N, 73.9857°E) somewhere in central Asia or (40.7484°S, 73.9857°W) in the South Pacific. A defensive parser should reject it; a careful publisher should always include sign or letter. If you must guess, North/East is the convention most software defaults to.

Can I tell the format from the number of characters?

Often, yes. Decimal degrees per coordinate: usually 10-15 characters including signs and decimal points. DMS: longer, with mixed degree/minute/second symbols. MGRS: 8-15 characters total. Plus Codes: 11 characters including the '+'. But character count isn't a strict test — context and the symbols (°, ', ", +, zone-band-letter pairs) are more reliable identifiers.

What if the coordinate uses commas as decimal separators (European convention)?

Common in continental European data: '40,7484' means 40.7484 in English notation. The pair separator then has to be something other than comma — usually a slash, semicolon, or pipe. Be defensive when parsing data from European sources: detect the locale (or the use of comma as decimal) before splitting the pair.

How do I know which datum a coordinate is in?

When unstated, WGS84 is the safe assumption for any coordinate published after the late 1990s. GPS readings, Google Maps, Mapbox, Apple Maps, and most modern datasets all use WGS84. When the source matters (surveying, legal boundaries, aviation), the dataset will specify. Older paper maps may use NAD27, OSGB36, Tokyo Datum, or other regional datums — the difference from WGS84 can be tens to hundreds of metres at any given point.

Why does my GPS reading show 7 decimal places when 6 is enough?

GPS hardware reports more decimals than the underlying measurement supports — the trailing digits are computational artifacts, not real position. Smartphone GPS is accurate to about 4.9 m under open sky (per GPS.gov); 6 decimal places of decimal degrees is ~11 cm at the equator, already finer than the accuracy. For human-shared coordinates, truncate to 5 or 6 decimal places. The 7th place is decoration.

Sources

  1. ISO — ISO 6709 — Standard representation of geographic point location · https://www.iso.org/standard/39242.html · Accessed .
  2. NOAA NGS — NCAT — Coordinate Conversion and Transformation Tool · https://www.ngs.noaa.gov/NCAT/ · Accessed .
  3. FAA — Aeronautical Information Manual — coordinate conventions · https://www.faa.gov/air_traffic/publications/atpubs/aim_html/ · Accessed .
  4. IHO — International Hydrographic Organization — maritime conventions · https://iho.int/ · Accessed .
  5. NGA — WGS84 reference and MGRS specification · https://earth-info.nga.mil/index.php?dir=wgs84 · Accessed .

Cite this article

APA format:

Steve K. (2026). How to Read Coordinates. Coordinately. https://coordinately.org/learn/how-to-read-coordinates

BibTeX:

@misc{coordinately_howtoread_2026,
  author = {K., Steve},
  title  = {How to Read Coordinates},
  year   = {2026},
  publisher = {Coordinately},
  url    = {https://coordinately.org/learn/how-to-read-coordinates},
  note   = {Accessed: 2026-06-05}
}