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Geocaching NSW: How GPS works

Degree and minutes

Many years ago, cartographers (map makers) knew that the world was a sphere. To help people figure out where they were located on this sphere, they devised a grid system called longitude and latitude.

The Earth rotates once every 24 hours around its axis. The points where this axis meets the surface are called the North and South Poles. Half way between the North and South Pole is an imaginary line that runs around the Earth called the equator.

Imaginary lines of latitude loop around the Earth parallel to the equator. The distance from the equator to the Poles is set at 90 degrees, because these points form a right angle at the Earth's core.

If you are standing half way between the equator and the South Pole, you are standing on the 45 degrees south line of latitude. The larger the value of the latitude, the closer you are to the pole.

Lines of longitude are circles that pass through the Poles, and are perpendicular to the equator.  The prime meridian (also known as 0 degrees longitude) was chosen in the 19th century to pass through Greenwich in the United Kingdom.  Lines of longitude range between 180 degrees east (of Greenwich) and 180 degrees west.

To describe your location anywhere on the Earth's surface, you use the lines of longitude and latitude as a grid.  For example, Canberra is located 35.3 degrees south of the equator and 149.1 degrees east of Greenwich – therefore, its location can be marked as S35.3° E149.1°.

Text courtesy of CSIRO Education