Longitude and Latitude

Longitude and latitude are part of the geographic coordinate system. This system was first invented by the Ancient Greek astronomer Hipparchus around 190-120 BC. It makes it easy to identify any place on Earth with a set of numbers, or coordinates. The system works simply. It splits the earth into a set of horizontal lines, called latitude, and vertical lines, called longitude.

Latitude lines are always parallel to each other, and to the equator, a line which runs across the exact middle of the earth, dividing it into North and South hemispheres. This can be pictured by standing an apple upright on the table, so the stem is perpendicular to the table, and then slicing the apple in half, parallel to the table. If the apple is sliced right in the middle, then it is sliced at the equator. Any other lines, up or down, parallel to the equator, are lines of latitude.

Longitude lines are similar, except they are vertical, running from the North Pole to the South Pole, always. These lines are not parallel. This can be pictured by standing an apple upright on the table as before, and then slicing it in half downwards, from the tip of the stem to the bottom of the apple. To make a different line of longitude, turn the knife, but still cut from the tip of the stem to the bottom.

An easy way to remember the difference is that latitude lines run laterally, or from side to side, and longitude lines run longways, from top to bottom. Taken together, latitude and longitude lines form a mesh around the entire earth. Each line is assigned a number. This number is given a corresponding degree, marked with the symbol: °.

The Equator, which runs east to west, right through the middle of the earth longways, and passes through countries like Ecuador, Brazil, the Democratic Republic of the Congo, and Kenya, is at 0-degrees latitude. There are 90 latitude lines north of the Equator, and the same number south of the Equator. If a place is referred to at a latitude of 36 in the Southern Hemisphere, you would write 36°S. The North Pole is 90°N, and the South Pole is 90°S.

The Prime Meridian, which runs north to south through places like the United Kingdom, France, Spain, Algeria, Mali, Ghana, and Antarctica, is 0 degrees-longitude. There are 179 longitude lines east of the Prime Meridian, beginning from zero, until they reach the longitude line which is directly opposite to the Prime Meridian on the globe. This is called the Antemeridian, and is marked as number 180. If you keep going east around the globe, you start counting down, until you reach the Prime Meridian from the other side, and are back at 0. If a place is referred to at a longitude of 121 to the west of the Prime Meridian, you would write 121°W.

Places which fall between the degrees are just given decimal points. A location exactly between a longitude of 20 and 21-east is written as 20.5°E.

This seems complicated, but makes it easy to refer to any place on Earth with these sets of numbers. For instance, New York City is 40.712 degrees north of the Equator and 74.005 degrees west of the Prime Meridian. The coordinates for New York City are 40.712°N, 74.005°W. It may seem difficult, but it is much faster and easier to use coordinates to help someone navigate from place to place. In the 21^st century, GPS systems, like those on cell phones, continue to use latitude and longitude.