Latitude vs Longitude: The Difference and How to Read Them

Latitude measures how far north or south of the Equator a place is, from 0° at the Equator to 90° at each pole. Longitude measures how far east or west of the Prime Meridian it is, from 0° at Greenwich, London, to 180° on the opposite side of the planet. Together they give every place on Earth a unique address: New York is about 40.7° N, 74.0° W.

Both are angles rather than distances, which is why they are written in degrees. Strictly, GPS and web maps use geodetic latitude on the WGS84 ellipsoid: the angle between the equatorial plane and a line perpendicular to the ellipsoid at your position. Because the Earth is slightly flattened, one degree of latitude is about 1% longer near the poles than near the Equator.

Coordinates come in three common forms. The steps to read them are the same: latitude first, then longitude, and the hemisphere tells you which way to go.

Decimal degrees (DD), for example 40.6892, -74.0445 (the Statue of Liberty):

1. The first number is latitude. 40.6892 is positive, so it is 40.6892° north of the Equator.
2. The second number is longitude. −74.0445 is negative, so it is 74.0445° west of the Prime Meridian.
3. The decimals are fractions of a degree. 0.6892° is not 68 minutes; it is 0.6892 × 60 = 41.35 minutes.

Degrees, minutes, seconds (DMS), for example 40°41'21.1"N 74°02'40.2"W:

1. Read 40°41'21.1"N as "40 degrees, 41 minutes, 21.1 seconds north". One degree has 60 minutes and one minute has 60 seconds.
2. Read 74°02'40.2"W the same way, west of Greenwich.
3. To compare with decimal degrees: 40 + 41/60 + 21.1/3600 = 40.6892. West makes the longitude negative: −74.0445.

On a paper or screen map with a grid:

1. Find the parallels (horizontal lines) on either side of your point and read their labels on the left or right edge. Estimate how far between them the point lies. That is the latitude.
2. Find the meridians (vertical lines) on either side and read their labels along the top or bottom edge. That is the longitude.
3. Add N or S for latitude and E or W for longitude, depending on which side of the Equator and Prime Meridian you are.

On a world map in the figure above, Austin reads 30.27° N on the left scale and 97.74° W on the top scale; Sydney reads 33.87° S and 151.21° E. To read the coordinates of any point precisely, click it on the latitude and longitude map.

A few memory tricks that work:

• "Lat is flat." Lines of latitude lie flat, running east-west like the rungs of a ladder. Latitude tells you how far up or down the ladder you are.
• "Long lines are long." Lines of longitude all run the full length from pole to pole, and they are all the same length.
• Latitude comes first in a coordinate pair, the same as in the alphabet.
• A number above 90 cannot be latitude. If you see 120 in the first position, the pair is swapped.

A useful sanity check is the U.S.: everywhere in the 50 states has a north latitude between about 18° (Hawaii) and 71° (northern Alaska) and a west longitude between about 66° (Maine) and 180°, except for the far western Aleutian Islands, which cross into east longitude. So a U.S. address in decimal degrees almost always looks like +lat, −lon.

How much ground does each decimal place represent? For latitude, and for longitude at the Equator:

Longitude distances shrink with latitude (see the next section), so at mid-latitudes the east-west values are smaller. In DMS, one second of latitude is about 31 m (101 ft) and one minute about 1.85 km (1.15 mi).

Five or six decimal places are plenty for most uses. More digits than your measurement supports suggest a precision that is not there: a phone fix accurate to 5 meters is not improved by writing it with eight decimals.

Parallels never meet, so one degree of latitude spans roughly the same distance everywhere, about 111 km (69 miles), varying by only about 1% between the Equator and the poles.

Meridians converge at the poles, so the length of one degree of longitude depends on latitude. It is roughly the length at the Equator multiplied by the cosine of the latitude:

This is why a "square" box of 1° by 1° is much narrower near the poles, and why equal steps in longitude are not equal distances. Flat world maps handle this in different ways; the map projections guide explains why some stretch the high latitudes and others squeeze them. Distance tools avoid the problem entirely by computing on the ellipsoid rather than from degree differences.

Most coordinate errors come from conventions rather than math:

• Signs. In decimal degrees, north and east are positive; south and west are negative. Austin, Texas is about 30.27, -97.74. Dropping the minus sign moves it to western China.
• Order. People and most web forms write latitude first: lat, lon. GeoJSON (RFC 7946) and many programming libraries use [lon, lat]. If a point lands in the ocean or the wrong hemisphere, a swap is the first thing to check.
• Letters versus signs. 30.27 N, 97.74 W and 30.27, -97.74 are the same point. Do not combine a minus sign with S or W.
• Valid ranges. Latitude must be between −90 and 90. A "latitude" of 120 means the values are swapped or corrupted.
• Formats. The same position can be written in decimal degrees, degrees-minutes-seconds, degrees and decimal minutes or UTM. See How Coordinate Formats Differ for worked conversions, and use the GPS coordinate converter to switch between them.

A practical workflow: get your own position with the latitude and longitude finder, which also reports the accuracy radius, and paste any coordinates you receive into the map before using them, so a swapped or missing sign is caught immediately.

A few named lines are defined by latitude or longitude:

• The Equator (0° latitude) divides the Northern and Southern Hemispheres. See where it crosses land on the equator map, or measure how far you are from the equator.
• The Tropics of Cancer and Capricorn lie at about 23.44° north and south, the latitudes where the sun can be directly overhead. They shift very slowly as Earth's axial tilt changes.
• The Arctic and Antarctic Circles lie at about 66.56°, the latitudes beyond which the sun can stay above or below the horizon for a full day.
• The Prime Meridian (0°) and the antimeridian (180°) divide the Eastern and Western Hemispheres. The International Date Line roughly follows the antimeridian but bends around island nations.

The point directly opposite you through Earth's center is your antipode. Its coordinates are −lat and lon ± 180°, keeping the longitude between −180 and 180. Most land antipodes fall in the ocean; the antipode finder shows yours.

Coordinates are only meaningful relative to a datum, which defines the ellipsoid and how it is fixed to Earth. GPS uses WGS84. North American surveying commonly uses NAD83, which differs from current WGS84 realizations by up to a couple of meters in the contiguous U.S. Older maps may use NAD27 or a national datum, where differences can reach tens or hundreds of meters.

For everyday navigation the WGS84/NAD83 difference does not matter. For surveying, property lines or combining old paper maps with GPS data, always note the datum along with the coordinates.