Every location on Earth can be written as a pair of numbers. The most common pair is latitude and longitude, measured in degrees. Surveyors, engineers and many GIS projects use UTM, which gives positions in metres instead. Both describe the same places; they're just different ways of counting.
Latitude and longitude
- Latitude is the angle north or south of the equator, from −90° (South Pole) to +90° (North Pole).
- Longitude is the angle east or west of the Prime Meridian through Greenwich, from −180° to +180°. Places in the Americas have negative longitudes.
New York City Hall is at about 40.7128° N, 74.0060° W, or 40.7128, −74.0060.
Three ways to write the same point
| Format | Example | Notes |
|---|---|---|
| Decimal degrees (DD) | 40.712800, −74.006000 | Used by GPS apps, web maps and most data |
| Degrees, minutes, seconds (DMS) | 40°42'46.08"N 74°00'21.60"W | Used on charts, deeds and older maps |
| Degrees, decimal minutes (DDM) | 40°42.7680'N 74°00.3600'W | Common in marine and aviation GPS |
To convert decimal degrees to DMS, take the whole degrees (40), multiply the remainder by 60 for minutes (0.7128 × 60 = 42.768, so 42), then multiply what's left by 60 for seconds (0.768 × 60 = 46.08). Going the other way: degrees + minutes ÷ 60 + seconds ÷ 3600.
Why a degree isn't a fixed distance
A degree of latitude is always about 111 km. A degree of longitude shrinks toward the poles, because the meridians meet there. Its length is roughly 111.32 km × cos(latitude):
This is why you can't measure distance or area directly in degrees, and why how many decimal places you keep matters. At the equator, the fifth decimal place (0.00001°) is about 1.1 m, and the sixth about 11 cm. Most GPS positions don't justify more than six.
How UTM coordinates work
The Universal Transverse Mercator system splits the world into 60 zones, each 6° of longitude wide, numbered eastward from 180°W. Inside each zone, positions are flat x/y distances in metres:
- Easting: metres east, with the zone's central meridian set to 500,000 m so values never go negative.
- Northing: metres north of the equator. In the southern hemisphere 10,000,000 m is added for the same reason.
- Latitude band: an optional letter for 8° bands, from C in the south to X in the north.
New York City Hall is 18T 583959E 4507351N: zone 18, band T, 583,959 m east and 4,507,351 m north. Because UTM is in metres, distances within a zone are simple to measure, which is why it's popular for site work. Across zone boundaries, it gets awkward; regional projects often use a state plane system or another local projection instead.
Common mistakes
- Swapped order. People write latitude first, but many formats, including GeoJSON and most software x/y fields, put longitude first. A swapped point near New York lands in Antarctica.
- Missing minus sign. Dropping the minus from −74.006 puts the point in Central Asia.
- Wrong datum. Coordinates are tied to a datum such as WGS84 or NAD83. In the US they differ by about a metre or two, enough to matter for surveys and parcels.
- Wrong UTM zone. The same easting and northing exist in all 60 zones. Always keep the zone number.
Frequently asked questions
Which format should I use?
Decimal degrees for data and software. DMS only when a document or client requires it. UTM or state plane when you need to measure in metres or feet.
How accurate is my phone's GPS?
Usually within about 5 m in open sky, worse near tall buildings and trees.
Why does my point appear in the ocean?
Usually swapped latitude and longitude, or a missing minus sign.
Thousands of coordinates to fix?
We clean, convert and map location data at scale.
Mixed formats, wrong datums, swapped columns: we turn them into one clean, mapped dataset.