a Uniform Resource Identifier (URI) for geographic locations using the 'geo' scheme name. A 'geo' URI identifies a physical location in a two- or three-dimensional coordinate reference system in a compact, simple, human-readable, and protocol-independent way.
The current revision of the vCard specification supports 'geo' URIs in a vCard's "GEO" property, and the GeoSMS standard uses 'geo' URIs for geotagging SMS messages. Android based devices support 'geo' URIs, although that implementation is based on a draft revision of the specification, and supports a different set of URI parameters and query strings.
A simple 'geo' URI might look like:
where the two numerical values represent latitude and longitude respectively, and are separated by a comma. If a third comma-separated value is present, it represents altitude. The 'geo' URI also allows for an optional "uncertainty" value, separated by a semicolon, representing the uncertainty of the location in meters, and is described using the "u" URI parameter. A 'geo' URI with an uncertainty parameter looks as follows:
A 'geo' URI may, for example, be included on a web page, as HTML:
<a href="geo:37.786971,-122.399677;u=35">Wikimedia Headquarters</a>
Coordinate reference systems
The default coordinate reference system (CRS) used is the World Geodetic System 1984 (WGS-84), for planet Earth although other CRS, once defined, may be specified, using the "crs" URI parameter, also separated by a semicolon. Such CRSs may include both other terrestrial systems and those for non-terrestrial coordinates such as those on the Moon or Mars.
A 'geo' URI for a hypothetical lunar CRS created in 2011 might be:
- "RFC 5870 - A Uniform Resource Identifier for Geographic Locations ('geo' URI)". Internet Engineering Task Force. 2010-06-08. Retrieved 9 June 2010.
- "RFC 6350 - vCard Format Specification". Internet Engineering Task Force. 2011-08-11. Retrieved 19 Jun 2012.
- "Android Intents List". google.com. Retrieved 2012-06-19.
- "Geourl.org". Geourl.org. Retrieved 2011-12-24.
- RFC 5870, section 8.3
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