The geo URI scheme is a Uniform Resource Identifier (URI) scheme defined by the Internet Engineering Task Force's RFC 5870 (published 8 June 2010) as: 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 geo URI is not to be confused with the former website of GeoURL (which had implemented ICBM addresses). Example A simple geo URI might look like: geo:37.786971,-122.399677 where the two numerical values represent latitude and longitude respectively, and are separated by a comma. They are coordinates of a horizontal grid (2D). If a third comma-separated value is present, it represents altitude; so, coordinates of a 3D grid. Coordinates in the Southern and Western hemispheres as well as altitudes below the coordinate reference system (depths) are signed negative with a leading dash. 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: geo:37.786971,-122.399677;u=35 A geo URI may, for example, be included on a web page, as HTML: Wikimedia Headquarters so that a geo URI-aware user agent such as a web browser could launch the user's chosen mapping service; or it could be used in an Atom feed or other XML file. Coordinate reference systems The values of the coordinates only make sense when a coordinate reference system (CRS) is specified. The default CRS is the World Geodetic System 1984 (WGS-84), and it is not recommended to use any other: The only justified use of other CRS today is, perhaps, to preserve projection in large-scale maps, as local UTM, or for non-terrestrial coordinates such as those on the Moon or Mars. The syntax and semantic of the CRS parameter, separated by a semicolon, is described at section 8.3 of RFC 5870. Examples: The Washington Monument's location expressed with UTM-zone 18N and its standard ID: geo:323482,4306480;crs=EPSG:32618;u=20