Coordinate Systems, Explained
All coordinate systems answer the same question — where on Earth? — but for different audiences: decimal degrees for software, DMS for navigation tradition, UTM/MGRS for meter-precise grid work, and Plus Codes, geohash or what3words for humans who need something shareable. The same spot, eight valid names.
One place, eight names
Take the Eiffel Tower. In decimal degrees it's 48.85837, 2.29448; in degrees-minutes-seconds, 48°51′30″N 2°17′40″E; in UTM, 31U 448252 5411935; in MGRS, 31UDQ4825211935; as a Plus Code, 8FW4V745+VQ; as a geohash, u09tunq; and what3words calls that exact 3-meter square ///prices.slippery.traps. Every one of these is correct — they're different encodings of the same point, each invented because some audience found the others awkward. Our coordinate converter translates between all of them in one click.
Latitude & longitude: decimal vs DMS
Latitude measures north–south from the equator (−90° to +90°), longitude east–west from Greenwich (−180° to +180°). Decimal degrees are the native language of software and APIs: one number per axis, easy to sort and compute with. Precision grows one digit at a time — 2 decimal places is ~1.1 km, 4 places ~11 m, 6 places ~11 cm. That's the quick way to judge any coordinate you're handed: count the decimals. DMS (degrees, minutes, seconds) is the same number in base-60, inherited from Babylonian astronomy via marine navigation; it survives on paper charts, in aviation, and in legal land descriptions. DDM (degrees + decimal minutes) is the compromise pilots and sailors actually use day-to-day.
Grid systems: UTM and MGRS
Degrees have an annoyance: a degree of longitude shrinks as you approach the poles, so distance math needs trigonometry. UTM fixes that by slicing Earth into 60 vertical zones and mapping each to a flat grid measured in meters — 'easting' and 'northing'. Within a zone, subtracting two coordinates gives you meters directly, which is why surveyors, hikers with paper maps, and scientists love it. MGRS is the military's re-packaging of UTM: the same grid, but written as a compact string whose length states its own precision — a 10-digit reference is a 1 m square, 6 digits a 100 m square. When rescue teams pass coordinates by radio, this self-describing precision is the point.
Codes for humans: Plus Codes, geohash, what3words
The newest systems optimize for sharing rather than math. Plus Codes (Open Location Code, by Google, fully open) turn lat/long into a short alphanumeric like V745+VQ Paris — designed for places without street addresses, and readable by Google Maps directly. Geohash nests the world into ever-smaller cells with a string that gets more precise per added character; developers use it for database indexing and proximity search because nearby places share prefixes. what3words names every 3 m square with three common words — easiest of all to say over a phone, though it's a proprietary system; see our what3words page for how we handle that honestly. None of these replaces latitude/longitude; they're friendlier envelopes around it.
Which should you use?
Sending a point to software or an API: decimal degrees, 5–6 decimals. Reading an aviation chart or legal deed: DMS. Working on foot with a paper topo map, or measuring distances by hand: UTM. Coordinating precisely over voice radio: MGRS. Sharing your position with another person: a Plus Code or a copied lat/long — both work in any maps app. And if the other person just needs to find you, skip coordinates entirely and send the map link or QR code from your location page; the best coordinate system is the one the recipient doesn't have to think about.