Tukuk-OSThe Idea in One Paragraph
Wrap the Earth in an imaginary cage of lines: circles running east-west (parallels of latitude) and half-circles running pole to pole (meridians of longitude). Any place on the surface is where one line from each family crosses, and the pair of line-numbers is its address. Latitude runs 0° at the equator to 90° at the poles, north or south. Longitude runs 0° at the prime meridian to 180° east or west — meeting again on the far side of the planet, which is exactly why the International Date Line sits there.
Why a Degree Is About 111 Kilometres
The Earth's meridional circumference is roughly 40,000 km, and a meridian is a full 360° — so one degree of latitude is 40,000 ÷ 360 ≈ 111 km, everywhere, always. That constant was no accident: the metre was originally defined as one ten-millionth of the distance from equator to pole. Longitude degrees are 111 km only at the equator; the parallels shrink as cos(latitude), so a degree of longitude in Norway covers barely half that, and at the poles it covers nothing at all — all meridians meet at a single point.
Minutes, Seconds, and Decimal Digits
Navigators subdivided each degree into 60 minutes and each minute into 60 seconds (so one arc-minute of latitude ≈ 1.85 km — exactly the nautical mile — and one arc-second ≈ 31 m) — sexagesimal accounting inherited from Babylon, which is also why circles have 360 degrees. Modern systems just write decimals: 5 decimal places is about 1.1 m, plenty to park a car on a coordinate. If two numbers differ by 0.001°, the places are roughly 111 metres apart at the equator — a useful gut-calibration when reading coordinates.
Why Longitude Took So Long to Get Right
Latitude is easy: measure the noon height of the Sun or the pole star and consult a table. Longitude requires knowing what time it is somewhere else — the reason "longitude clocks" (marine chronometers) made John Harrison famous and why navigators kept sailing into cliffs. The prime meridian itself is pure convention: every nation's mapmaker used their own capital until the 1884 conference picked Greenwich, largely because most world charts were already drawn there by British shipbuilders. When you enter a coordinate today, you are using an agreement that is only about 140 years old — and coordinates you see online are almost always in the WGS84 reference frame, the ellipsoid GPS runs on, which differs from older local maps by anything from a few metres to over a kilometre.
Try It Yourself
On our route planner every search result returns its latitude and longitude, and the two boxes accept raw coordinates directly — paste any pair and press Go. Look up your own home, then your country's capital, and compute the rough north-south distance from the latitude difference alone (×111 km). It works better than most people expect, and it is the same arithmetic that let sailors estimate home. For the cast of characters living at each coordinate, the World Cities profiles show where the great cities actually sit.