Do you ever see people wandering around the Harbury district with a GPS acting as if they are looking for something. Well they are! It is the hobby of geocaching, a high tech hide and seek.
Geocaching is an outdoor treasure-hunting game in which the participants use a Global Positioning System (GPS) receiver or other navigational techniques to hide and seek containers (called "geocaches" or "caches") anywhere in the world. A typical cache is a small waterproof container containing a logbook and "treasure," usually toys or trinkets of little value.
Currently over 700,000 geocaches are registered on various websites devoted to the pastime. Geocaches are currently placed in over 100 countries around the world and on all seven continents, including Antarctica.
The GPS constellation in motion with the Earth rotating to illustrate GPS function as applied in Geocaching
Geocaching is similar to the 150-year-old letterboxing, which uses references to landmarks and clues embedded in stories. However, geocaching was imagined shortly after the removal of Selective Availability from GPS on May 1, 2000 because the improved accuracy of the system allowed for a small container to be specifically placed and located. The first documented placement of a GPS-located cache took place on May 3, 2000, by Dave Ulmer of Beavercreek, Oregon. The location was posted on the Usenet newsgroup sci.geo.satellite-nav as [show location on an interactive map] 45°17.460′N 122°24.800′W / 45.291°N 122.413333°W / 45.291; -122.413333. By May 6, 2000, it had been found twice and logged once (by Mike Teague of Vancouver, Washington). According to Dave Ulmer's message, the original stash was a black plastic bucket buried most of the way in the ground and contained software, videos, books, food, money, and a slingshot.
 Origin of the name
The activity was originally referred to as GPS stash hunt or gpsstashing. This was changed after a discussion in the gpsstash discussion group at eGroups (now Yahoo!). On May 30, 2000, Matt Stum suggested that "stash" could have negative connotations, and suggested instead "geocaching."
Geocache Pfalz Werla in Germany
For the traditional geocache, a geocacher will place a waterproof container, containing a log book (with pen or pencil) and trinkets or some sort of treasures, then note the cache's coordinates. These coordinates, along with other details of the location, are posted on a website. Other geocachers obtain the coordinates from the Internet and seek out the cache using their GPS handheld receivers. The finding geocachers record their exploits in the logbook and online. Geocachers are free to take objects from the cache in exchange for leaving something of similar or higher value, so there is treasure for the next person to find.
Microcache hidden and found beside the Roman Colosseum.
Typical cache treasures are not high in monetary value but may hold personal value to the finder. Aside from the logbook, common cache contents are unusual coins or currency, small toys, ornamental buttons, CDs, or books. Also common are objects that are moved from cache to cache, such as Travel Bugs or Geocoins, whose travels may be logged and followed online. Cachers who initially place a Travel Bug or Geocoin often assign specific goals for their trackable items. One such goal could be to pass it westward across the continent. Occasionally, higher value items are included in geocaches, normally reserved for the first to find, or "FTF", or in locations which are harder to reach.
A Travel Bug
Geocache container sizes range from film canisters often called "microcaches," too small to hold anything more than a tiny paper log, to five-gallon buckets or even larger containers.
If a geocache has been vandalized or stolen, it is said to have been "muggled" or "plundered." The former term plays off the fact that those not familiar with geocaching are called "geo-muggles" or just muggles, a term popularised by the Harry Potter series of books.
If a cacher discovers that a cache has been muggled, it can be logged as needing maintenance, which sends an e-mail to the cache owner so it can be repaired, replaced, or archived (deactivated).
Geocaches vary in size, difficulty, and location. Simple caches are often called "drive-bys," "park 'n grabs" ("PNGs"), or "cache and dash." Geocaches may also be complex, involving lengthy searches or significant travel. Examples include staged multi-caches; underwater caches, caches located 50 feet (15 m) up a tree, caches found only after long offroad drives, caches on high mountain peaks, caches located in challenging environments (such as Antarctica  or north of the Arctic Circle), and magnetic caches attached to metal structures and/or objects. Different geocaching websites list different variations per their own policies (e.g. Geocaching.com does not list new Webcam, Virtual, Locationless, or Moving geocaches).
A small traditional geocache in the Czech Republic.
Variations of geocaches include:
* Traditional: The basic cache type, a traditional cache must include a log book of some sort. It may or may not include trade or trackable items. A traditional cache is distinguished from other cache variations in that the geocache is found at the coordinates given and involves only one stage.
* Multi-cache: This variation consists of multiple discoveries of one or more intermediate points containing the coordinates for the next stage; the final stage contains the log book and trade items.
* Offset: This cache is similar to the multi-cache except that the initial coordinates are for a location containing information that encodes the final cache coordinates. An example would be to direct the finder to a plaque where the digits of a date on the plaque correspond to coordinates of the final cache.
* Night Cache: These multi-stage caches are designed to be found at night and generally involve following a series of reflectors with a flashlight to the final cache location.
* Mystery/puzzle: This cache requires one to discover information or solve a puzzle to find the cache. Some mystery caches provide a false set of coordinates with a puzzle that must be solved to determine the final cache location. In other cases, the given location is accurate, but the name of the location or other features are themselves a puzzle leading to the final cache. Alternatively, additional information is necessary to complete the find, such as a padlock combination to access the cache.
* Letterbox Hybrid: A letterbox hybrid cache is a combination of a geocache and a letterbox in the same container. A letterbox has a rubber stamp and a logbook instead of tradable items. Letterboxers carry their own stamp with them, to stamp the letterbox's log book and inversely stamp their personal log book with the letterbox stamp. The hybrid cache contains the important materials for this and may or may not include trade items. Whether the letterbox hybrid contains trade items is up to the owner.
* Locationless/Reverse: This variation is similar to a scavenger hunt. A description is given for something to find, such as a one-room schoolhouse, and the finder locates an example of this object. The finder records the location using their GPS hand-held receiver and often takes a picture at the location showing the named object and his or her GPS receiver. Typically others are not allowed to log that same location as a find.
* Moving/Traveling: Similar to a traditional geocache, this variation is found at a listed set of coordinates. The finder uses the log book, trades trinkets, and then hides the cache in a different location. By updating this new location on the listing, the finder essentially becomes the hider, and the next finder continues the cycle.
A Geocacher finding a Virtual Cache at McMurdo Station, Antarctica
* Virtual: Caches of this nature are coordinates for a location that does not contain the traditional box, log book, or trade items. Instead, the location contains some other described object. Validation for finding a virtual cache generally requires you to email the cache hider with information such as a date or a name on a plaque, or to post a picture of yourself at the site with GPS receiver in hand.
* Earthcache: A type of virtual-cache which is maintained by the Geological Society of America. The cacher usually has to perform a task which teaches him/her an educational lesson about the earth science of the cache area.
* Webcam: Similar to a virtual cache; there is no container, log book, or trade items for this cache type. Instead, the coordinates are for a location with a public webcam. Instead of signing a log book, the finder is often required to capture their image from the webcam for verification of the find.
* Event Cache: This is a gathering organized and attended by geocachers. Physical caches placed at events are often active only for the event date.
* Cache-In Trash-Out (CITO) Events: This variation on event caching is a coordinated activity of trash pickup and other maintenance to improve the environment.
* Mega Event: An event that is attended by over 500 people. Mega Events are typically annual events, usually attracting geocachers from all over the world.
* Wherigo cache: A Wherigo cache is similar to a multi-stage cache hunt that uses a Wherigo cartridge to guide the player. The player plays the cartridge and finds a physical cache sometime during cartridge play, usually at the end. Not all Wherigo cartridges incorporate geocaches into game play. Wherigo caches are unique to the geocaching.com website.
 Obtaining data
GPX files contain information such as a cache description and information about recent visitors to the cache. Geocachers may upload geocache data (also known as waypoints) from various websites in various formats, most commonly in file-type GPX, which uses XML. Some websites allow geocachers to search (build queries) for multiple caches within a geographic area based on criteria such as Zip Code or coordinates, downloading the results as an email attachment on a schedule. Although often a time-consuming process with many possibilities for error, appropriate client software allows cachers to build individual GPX files.
 Converting and filtering data
A variety of geocaching applications are available for geocache data management, file-type translation, and personalization. Geocaching software can assign special icons or search (filter) for caches based on certain criteria (e.g. distance from an assigned point, difficulty, date last found).
Paperless geocaching employs PDAs or other electronic devices to carry geocache information instead of paper. Various applications are able to directly upload and read GPX files without further conversion. Newer GPS devices released by Garmin have the ability to read GPX files directly, thus eliminating the need for a PDA. The release of numerous cellphones which have a GPS chip built in, has enabled another platform for paperless geocaching. An example of this is the iPhone as well as some Nokia and Blackberry devices for which a Geocache Navigator application is available .
Individual geocaching websites have developed their own guidelines for acceptable geocache publications. Though not universally required, the Geocacher's Creed provides ethical search guidelines. Government agencies and others responsible for public use of land often establish their own guidelines for geocaching. Generally accepted rules are to not endanger others, to minimize the impact on nature, to respect private property, and to avoid public alarm.
Cachers have been approached by police and questioned when they were seen as acting suspiciously. Other times, investigation of a cache location after suspicious activity was reported has resulted in police and bomb squad discovery of the geocache. A number of caches have been destroyed by bomb squads.
The examples and perspective in this article may not represent a worldwide view of the subject. Please improve this article or discuss the issue on the talk page.
Numerous websites list geocaches around the world. In the United States, where most geocaching services are hosted, only a cache's coordinates are in public domain. Other cache information, including the description, is protected by copyright law. Geocaching websites vary in active protection of cache data.
 First page
The first website to list geocaches was announced by Mike Teague on May 8, 2000. On September 2, 2000, Jeremy Irish emailed the gpsstash mailing list that he had registered the domain name geocaching.com and had setup his own Web site. He copied the caches from Mike Teague's database into his own. On September 6, Mike Teague announced that Jeremy Irish was taking over cache listings.
Typical GPS receivers as used to locate the co-ordinates of a Geocache.
A large site is Geocaching.com, owned by Groundspeak Inc., which began operating on September 2, 2000. With a worldwide membership, Geocaching.com lists hundreds of thousands of caches. As of November 2008 over 700,000 caches had been hidden with more created daily. Each cache is reviewed by regional cache reviewers before publication with an emphasis on family-oriented caching. Free basic membership allows users to see coordinates for most caches in its database; premium membership includes a fee for additional features, including advanced search tools and caches designed for premium members.
Geocaching.com no longer lists new caches without a physical container, including locationless/reverse and webcam; however, older caches of these types have been grandfathered in (except for locationless/reverse, which are completely archived). Earthcaches are the exception to the no-container rule; they are caches in which players must answer geological questions to complete the cache. Groundspeak created a waymarking website to handle all other non-physical caches.
Geocaching.com also supports the discovery of benchmarks, which are a location "known to a high degree of accuracy" Sometimes these can be metal disks, radio towers, or a bolt in central locations or on a highway. Their main purpose is for surveying an area. Geocaching gives the longitude and latitude to this location and the user must rely on given clues to find the benchmark.
Navicache.com started as a regional listing service around February 2001, but quickly gained popularity among those looking for a less restrictive alternatives to what was currently available. While many of Navicache.com's listings have been posted to other sites, they also offer many unique listings. Navicache.com also lists nearly any type of geocache (within reason) and does not charge to access any of the caches listed in their database. While all submissions are reviewed and approved, Navicache is more liberal in approving caches believing that the pastime belongs to participants rather than a governing agency.
Terracaching seeks to provide high-quality caches made so by the difficulty of the hide or from the quality of the location. Membership is managed through a sponsorship system, and each cache is under continual peer review from other members. TerraCaching.com embraces virtual caches alongside traditional/multi-stage caches and includes many locationless caches among the thousands of caches in its database.
 Other sites
In many countries there are regional geocaching sites, but these do mostly only compile lists of caches in the area from the three main sites. Many of them also accept unique listings of caches for their site, but these listings tend to be less popular than the international sites. There are some exceptions though, e.g. in the former Soviet Union the site geocaching.su remains popular because it accepts listings in the cyrillic alphabet.