The exploration of space has brought us many benefits. The most over-used examples are of course Velcro and non-stick frying pans, but better examples would be satellite communication, accurate weather forecasting based on satellite imagery, and of course satellite navigation. The Global Positioning System, or GPS as it is commonly known, uses a fleet of satellites owned and operated by the United States Air Force, but made freely available to the public all over the world. The GPS satellites orbit the Earth at an altitude of just over 20,000 kilometres, transmitting microwave signals that can be picked up by ground-based receivers.
Since the orbits of the satellites are fixed, and are arranged in such a way that at least six satellites are always in line of sight from any point on Earth, the accurate time signatures encoded in the signals allow the receiver to calculate its position on the surface of the Earth with a high degree of precision, typically within a few metres. Contrary to popular belief, since the year 2000 civilian GPS navigation is just as accurate as the systems used by the military.
Since it first became available in the mid 1990s, GPS has been used for accurate navigation in all forms of transport from military and commercial ships and aircraft to the increasingly popular car satellite navigation systems that are now fitted as standard to many new models.
Like all electronic gadgets, as the popularity of GPS navigation has increased, the receivers have become cheaper and smaller. Self-contained GPS receiver units have become small and cheap enough that they are now routinely included in new mobile phones, and are now finding their way into digital cameras. GPS units are also available as add-on accessories from camera manufacturers and third-party companies, and the increasing popularity and affordability of this technology has led to the growth of a new application of digital photography, known as Geotagging.
In its broadest sense Geotagging simply means adding geographical location data, usually latitude, longitude and altitude, to an image or other type of record, but by popular usage it has come to mean adding GPS co-ordinates to the EXIF data accompanying a digital photo, which allows some popular mapping programs, most notably Google Earth, to display that photo at the position where it was taken. It's a fun way to catalogue and share your travel photographs, and can also be useful for a range of serious photographic applications, such as surveying and wildlife research.