A 'geo' URI is a URI scheme

URI scheme

In the field of computer networking, a URI scheme is the top level of the Uniform Resource Identifier naming structure. All URIs and absolute URI references are formed with a scheme name, followed by a colon character , and the remainder of the URI called the scheme-specific part...

 defined by the Internet Engineering Task Force

Internet Engineering Task Force

The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...

's RFC

Request for Comments

In computer network engineering, a Request for Comments is a memorandum published by the Internet Engineering Task Force describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems.Through the Internet Society, engineers and...

 5870 (published 8 June 2010) as:

a Uniform Resource Identifier

Uniform Resource Identifier

In computing, a uniform resource identifier is a string of characters used to identify a name or a resource on the Internet. Such identification enables interaction with representations of the resource over a network using specific protocols...

 (URI) for geographic locations using the 'geo' scheme name

URI scheme

In the field of computer networking, a URI scheme is the top level of the Uniform Resource Identifier naming structure. All URIs and absolute URI references are formed with a scheme name, followed by a colon character , and the remainder of the URI called the scheme-specific part...

. A 'geo' URI identifies a physical location in a two- or three-dimensional coordinate reference system in a compact, simple, human-readable, and protocol

Communications protocol

A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...

-independent way.

The current revision of the vCard

VCard

vCard is a file format standard for electronic business cards. vCards are often attached to e-mail messages, but can be exchanged in other ways, such as on the World Wide Web or Instant Messaging...

 specification supports 'geo' URIs in a vCard's "GEO" property, and the GeoSMS

GeoSMS

GeoSMS is a specification for geotagging SMS messages.It works by embedding locations in the message text, where the locations are formatted as 'geo' URIs as defined in RFC 5870....

 standard uses 'geo' URIs for geotagging SMS messages.

A 'geo' URI is not to be confused with the site GeoUrl (which implements ICBM address

ICBM address

ICBM address or missile address is hacker slang for one's longitude and latitude when placed in a signature or another publicly available file.- Origin :...

).

Example

A simple 'geo' URI might look like:

geo:37.786971,-122.399677

where the two numerical values represent latitude

Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

 and longitude

Longitude

Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

 respectively, and are separated by a comma

Comma

A comma is a type of punctuation mark . The word comes from the Greek komma , which means something cut off or a short clause.Comma may also refer to:* Comma , a type of interval in music theory...

. If a third comma-separated value is present, it represents altitude

Altitude

Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

. The 'geo' URI also allows for an optional "uncertainty" value, separated by a semicolon

Semicolon

The semicolon is a punctuation mark with several uses. The Italian printer Aldus Manutius the Elder established the practice of using the semicolon to separate words of opposed meaning and to indicate interdependent statements. "The first printed semicolon was the work of ... Aldus Manutius"...

, 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

HTML

HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....

:

Wikimedia Headquarters

so that a 'geo' URI-aware user agent

User agent

In computing, a user agent is a client application implementing a network protocol used in communications within a client–server distributed computing system...

 such as a web browser

Web browser

A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...

 could launch the user's chosen mapping service; or it could be used in an Atom

Atom (standard)

The name Atom applies to a pair of related standards. The Atom Syndication Format is an XML language used for web feeds, while the Atom Publishing Protocol is a simple HTTP-based protocol for creating and updating web resources.Web feeds allow software programs to check for updates published on a...

 feed or other XML

XML

Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....

 file.

Coordinate reference systems

The default coordinate reference system (CRS) used is the World Geodetic System 1984

World Geodetic System

The World Geodetic System is a standard for use in cartography, geodesy, and navigation. It comprises a standard coordinate frame for the Earth, a standard spheroidal reference surface for raw altitude data, and a gravitational equipotential surface that defines the nominal sea level.The latest...

 (WGS-84), for planet Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 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

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 or Mars

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

.

A 'geo' URI for a hypothetical lunar CRS created in 2011 might be:

geo:37.786971,-122.399677;u=35;crs=Moon-2011

The order in which the semicolon-separated parameters occur is not significant, and 'crs' parameter values are case-insensitive

Case sensitivity

Text sometimes exhibits case sensitivity; that is, words can differ in meaning based on differing use of uppercase and lowercase letters. Words with capital letters do not always have the same meaning when written with lowercase letters....

, so the above example is exactly equivalent to:

geo:37.786971,-122.399677;crs=moon-2011;u=35