What Are Latitude and Longitude? A Complete Beginner's Guide
Latitude and longitude are the universal coordinate system for describing any point on Earth. This guide explains how they work, how to read them, and where they come from.
Latitude and longitude are the two numbers that let you pinpoint any location on Earth. From ordering a pizza to tracking a hurricane, every modern location system depends on this pair of angles. This guide walks you through what they are, how to read them in both common formats, where the system came from, and how precise the numbers really are.
The idea behind geographic coordinates
Imagine wrapping the Earth in a grid. Latitude lines run east-west and measure how far north or south a point is from the equator. Longitude lines run north-south and measure how far east or west a point is from the prime meridian at Greenwich, England. Together they form a spherical coordinate system: any spot on the planet's surface gets a unique pair of angles. Unlike a street address, which depends on local naming conventions, a lat/lng pair works everywhere — in the middle of an ocean, on top of a mountain, or in a city that has never been mapped by name. That universality is why every GPS receiver, every web map, and every aviation and shipping system speaks latitude and longitude underneath.
Reading latitude
Latitude is measured in degrees from -90 degrees at the South Pole to +90 degrees at the North Pole, with the equator at 0 degrees. Points in the Northern Hemisphere are positive (or marked N); points in the Southern Hemisphere are negative (or marked S). Paris sits at about 48.86° N, Sydney at about 33.87° S. One degree of latitude is roughly 111 kilometres everywhere on Earth, because latitude lines are all the same length — they are parallel circles, which is why latitude is sometimes called a 'parallel'. This constancy makes latitude the easier of the two coordinates to reason about: move one degree north and you have travelled about 111 km, wherever you are.
Reading longitude
Longitude is measured from -180° to +180°, with the prime meridian at Greenwich, UK, defined as 0°. East of Greenwich values are positive (E); west of it they are negative (W). New York City is about -74.01°, Tokyo about 139.65°. Unlike latitude, a degree of longitude is not a fixed distance: longitude lines (meridians) converge at the poles. At the equator a degree of longitude is about 111 km, the same as latitude, but at 60° latitude it is only about 56 km, and at the poles it is zero. This is why converting a longitude difference into kilometres always requires knowing the latitude too.
Decimal degrees vs degrees-minutes-seconds
The same location can be written two ways. Decimal degrees (DD) write each coordinate as a single decimal number: 48.8583° N, 2.2945° E for the Eiffel Tower. Degrees-minutes-seconds (DMS) splits each degree into 60 minutes and each minute into 60 seconds: 48° 51' 30" N, 2° 17' 40" E. Decimal degrees are easier for computers and calculations; DMS is traditional on nautical charts and older maps. Converting is simple arithmetic: decimal = degrees + minutes/60 + seconds/3600. So 48° 51' 30" becomes 48 + 51/60 + 30/3600 = 48.8583°. Going the other way, the fractional part 0.8583 × 60 = 51.5 minutes, and 0.5 × 60 = 30 seconds.
Datums: why WGS84 matters
A latitude and longitude pair is meaningless without a datum — the mathematical model of the Earth's shape it refers to. The Earth is not a perfect sphere but an oblate ellipsoid, slightly flattened at the poles, and different datums model that ellipsoid slightly differently. The global standard today is WGS84 (World Geodetic System 1984), used by GPS and virtually all web maps. Older regional datums can shift the same lat/lng pair by tens or even hundreds of metres relative to WGS84. In practice this means: if you are given coordinates, assume WGS84 unless told otherwise, and if you are mixing data from old paper maps with GPS, check the datum — a mismatch is one of the most common causes of 'wrong' coordinates.
A brief history of the system
Latitude has been measurable since antiquity: Greek astronomers like Hipparchus worked out that the height of the sun or the Pole Star above the horizon reveals your latitude. Longitude was far harder, because it requires knowing the time difference between your location and a reference meridian — and accurate clocks did not exist. The problem was famously solved in the 18th century when John Harrison built marine chronometers accurate enough to carry reference time aboard ships. The prime meridian itself was fixed by international agreement at the International Meridian Conference in Washington, D.C., in 1884, which adopted Greenwich as 0° longitude. The modern WGS84 datum, established in 1984 and refined since, gives the whole system a consistent global reference frame.
Precision: what the decimal places mean
Not all coordinates are equally precise, and the number of decimal places tells you the implied precision. Roughly: one decimal place is about 11 km, two about 1.1 km, three about 110 m, four about 11 m, five about 1.1 m, and six about 0.11 m at the equator. A typical smartphone GPS delivers 3–5 metre accuracy in open sky, so quoting more than five or six decimals from a phone is false precision — the extra digits are noise. When you see coordinates with six decimals, read them as 'accurate to about the size of a dinner plate'; with two decimals, 'accurate to about a kilometre'. Matching the decimals to your actual measurement quality is a small habit that prevents big misunderstandings.
Finding your own coordinates
On a smartphone, open your maps app, long-press (or drop a pin on) any location, and the app will display its latitude and longitude — usually in decimal degrees. On a desktop, right-clicking a point in most web maps shows the same. If you work with coordinates often, a converter tool that switches between decimal degrees, DMS, UTM, MGRS and Plus Codes saves constant manual arithmetic; the key conversions to know are DD to DMS (multiply the fraction by 60 twice) and the reverse (divide minutes by 60 and seconds by 3600). Whatever format you receive coordinates in, convert once to decimal degrees before doing any math — every distance and bearing formula expects decimal degrees.
Common mistakes to avoid
Four mistakes cause most coordinate confusion. First, swapping latitude and longitude: latitude always comes first in the pair and ranges only ±90°, so a 'latitude' of 139° is really a longitude. Second, mixing datums, as described above. Third, forgetting that west and south are negative in decimal notation — dropping a minus sign can teleport your point to the wrong hemisphere. Fourth, assuming online map pins are exact: a pin dropped by hand on a phone screen is easily 10–50 metres off. For navigation to a trailhead or a rural address, that is fine; for surveying or property boundaries, it is not — use proper equipment and never rely on consumer coordinates for legal boundaries.
Try it yourself
Put this into practice: convert between decimal degrees and DMS formats, look up the coordinates of any place, or convert coordinates between formats — all three are free and run entirely in your browser.
Frequently asked questions
How precise are lat/lng coordinates from a phone?
A standard phone GPS gives 3–5 metre precision in open sky, worse among tall buildings or under dense tree cover. Six decimal places imply about 0.11 m, which is more precise than the phone can actually measure — treat the last digits as noise.
Why is the prime meridian at Greenwich?
The International Meridian Conference in Washington, D.C., in 1884 adopted Greenwich as the 0° reference. Britain was then the leading maritime power and most nautical charts already used Greenwich, so it was the practical choice.
What is WGS84?
The World Geodetic System 1984 is the global reference frame — the ellipsoid model and coordinate system — used by GPS and nearly all web maps. Coordinates without a stated datum are almost always WGS84 today.
Why are some longitudes negative?
In decimal notation, east of Greenwich is positive and west is negative. So New York at 74° W is written -74.01°. The minus sign is just shorthand for 'west'.
What happens at the poles and the 180° meridian?
At the poles longitude is undefined — every meridian meets there, so only latitude (±90°) matters. The 180° meridian, opposite Greenwich in the Pacific, is where +180° and -180° meet; crossing it flips the sign but you stay in the same place.
Sources & data
Authoritative references used to research and verify this article: