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Reverse geocoding is the process of using latitude and longitude coordinates to find specific geographical features or street addresses. This process is the opposite of the more common geocoding method. In standard geocoding, the features and streets are mapped first and then assigned a coordinate. Reverse geocoding fills in the gaps in standard geocoded coordinate information so only a few spots are needed to find a location.
The process of standard geocoding and reverse geocoding go together. Using standard geocoding techniques, the beginning and endpoint of a street have exact latitude and longitude coordinates laid out. Geocoding software lays out the street in a mapping program, and the user enters the first and last street address for the area. Using reverse geocoding, the program extrapolates the street numbers of the houses along the mapped road using coordinates and relative position.
Reverse geocoding is considered an important step in many navigation technologies. Things like on-board vehicle navigation and Enhanced 911 service rely on reverse geocoding to estimate the location of destinations. Very few areas have had every house on every street geocoded, so services rely on reversed information to locate the destination point for vehicles. The reversed location may be several feet off the actual, but it is generally close enough that a person can find the true location by normal means.
This process is also useful to outdoorsmen. They are able to find their coordinates and use them as their base point. Information about known sites near that point are then relayed back to them. This makes it easy to find known spots, such as a fishing spot or hiking trail, which have already been found with standard geocoding. With a full geographic information system available, it is also possible to find other nearby locations of interest, like a highway or river.
As with many geographic information systems, reverse geocoding has seen its share of controversy. By using preexisting maps, it is possible to locate people or areas that were not intended to be found. Many forms of confidential studies and experiments rely on subjects' relative proximity to each other or a central point. In these studies, it isn’t uncommon to publish maps showing the locations of the subjects. These maps intentionally have few features, but when fed through a reverse geocoding process, it is possible to locate the subject’s position.
When this ability is combined with other geographic systems, the problems become more pronounced. Anonymous locations of people and places are relatively easy to find; then, extrapolated information from public information can find even more about the subject. This can allow people to easily track others and learn shopping or driving habits.