geo

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Revision as of 19:32, 11 December 2006 by Tantek (talk | contribs) (added geo-extension-strawman reference and Related Work section)
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geo

geo (working name, pronounced "gee-oh") is a simple format for marking up geographic latitude longitude information, suitable for embedding in (X)HTML, Atom, RSS, and arbitrary XML. geo is a 1:1 representation of the "geo" property in the vCard standard (RFC2426) in XHTML, one of several open microformat standards.

Draft Specification

Editor/Author

Tantek Çelik, Technorati, Inc.

Copyright

This specification is (C) 2005-2024 by the authors. However, the authors intend to submit (or already have submitted, see details in the spec) this specification to a standards body with a liberal copyright/licensing policy such as the GMPG, IETF, and/or W3C. Anyone wishing to contribute should read their copyright principles, policies and licenses (e.g. the GMPG Principles) and agree to them, including licensing of all contributions under all required licenses (e.g. CC-by 1.0 and later), before contributing.

Patents

This specification is subject to a royalty free patent policy, e.g. per the W3C Patent Policy, and IETF RFC3667 & RFC3668.

Inspiration and Acknowledgments

Thanks to everyone who participated in the Geo Microformat BOF at O'Reilly's Where 2.0 conference, and in particular to Nat Torkington and Vee McMillen of O'Reilly for arranging and hosting the BOF. Thanks to Chris Hibbbert for providing the real world geo-caching example.

Introduction and Background

The vCard standard (RFC2426), has been broadly and interoperably implemented (e.g. Apple's Address Book application). The hCard microformat has similarly received significant adoption, from numerous sites publishing the format, to hCard to vCard proxies, to clientside javascript parsers.

At the Where 2.0 conference in June 2005, there was widespread recognition that the community needed a way to simply and easily publish visible, extractable, geographic location information on the Web, given how often bloggers, and numerous other sites publish such information. The geo microformat BOF discussed this very topic, and concluded with a consensus decision to just try using geo from vCard/hCard.

This specification introduces the geo microformat, which is a 1:1 representation of the aforementioned geo property from the vCard standard, by simply reusing the geo property and sub-properties as-is from the hCard microformat.

Publishers can both embed geo addresses directly in their web pages and feeds, as well as markup existing latitude/longitude coordinates in the context of the rest of the information in their web pages and feeds.

If the publisher knows and is publishing the name of the location in addition to its geo lat/long, then the publisher MUST use hCard instead of just geo to publish the name and geo lat/long of the location.

If the publisher knows and is publishing the address of the location, OR if the address of the location was what was actually entered by a human, and the publisher simply turned that into lat/long using some sort of a service, then the publisher SHOULD use adr to publish the actual human entered address information since that communicates far more semantic information than a simple geo lat/long coordinate.

Semantic XHTML Design Principles

Note: the Semantic XHTML Design Principles were written primarily within the context of developing hCard and hCalendar, thus it may be easier to understand these principles in the context of the hCard design methodology (i.e. read that first). Tantek

XHTML is built on XML, and thus XHTML based formats can be used not only for convenient display presentation, but also for general purpose data exchange. In many ways, XHTML based formats exemplify the best of both HTML and XML worlds. However, when building XHTML based formats, it helps to have a guiding set of principles.

  1. Reuse the schema (names, objects, properties, values, types, hierarchies, constraints) as much as possible from pre-existing, established, well-supported standards by reference. Avoid restating constraints expressed in the source standard. Informative mentions are ok.
    1. For types with multiple components, use nested elements with class names equivalent to the names of the components.
    2. Plural components are made singular, and thus multiple nested elements are used to represent multiple text values that are comma-delimited.
  2. Use the most accurately precise semantic XHTML building block for each object etc.
  3. Otherwise use a generic structural element (e.g. <span> or <div>), or the appropriate contextual element (e.g. an <li> inside a <ul> or <ol>).
  4. Use class names based on names from the original schema, unless the semantic XHTML building block precisely represents that part of the original schema. If names in the source schema are case-insensitive, then use an all lowercase equivalent. Components names implicit in prose (rather than explicit in the defined schema) should also use lowercase equivalents for ease of use. Spaces in component names become dash '-' characters.
  5. Finally, if the format of the data according to the original schema is too long and/or not human-friendly, use <abbr> instead of a generic structural element, and place the literal data into the 'title' attribute (where abbr expansions go), and the more brief and human readable equivalent into the element itself. Further informative explanation of this use of <abbr>: Human vs. ISO8601 dates problem solved

Format

Singular Properties

Note that all the properties in geo are singular properties, and thus the first descendant element with that class should take effect, any others being ignored.

Human vs. Machine readable

If an <abbr> element is used for a property, then the title attribute of the <abbr> element is the value of the property, instead of the contents of the element, which instead provide a human presentable version of the value.

Value excerpting

Sometimes only part of an element which is the equivalent for a property should be used for the value of the property. For this purpose, the special class name value is used to excerpt out the subset of the element that is the value of the property. See hCard for details on this.

Root Class Name

The root class name for an geo location is geo.

Property List

This is the list of properties in geo, taken from hCard:

  • latitude
  • longitude

XMDP Profile

See hcard-profile for the XMDP profile of hCard which contains the above complete list of properties, with references to their RFC 2426 definitions.

Parsing Details

See hCard parsing, with the only difference being that "geo" is the root class name, rather than "vcard".

Examples

This section is informative.

Example from RFC2426

Section 3.4.2 of RFC2426 has a simple geo example: 

GEO:37.386013;-122.082932

this vCard fragment as a geo, as first documented on the hCard examples page: 

<span class="geo">
 <span class="latitude">37.386013</span>, 
 <span class="longitude">-122.082932</span>
</span>

this geo could be displayed as:

37.386013, -122.082932


Real world geo example

Here is a sample of published lat/long info (from geocaching: Noble Steed): 

N 37° 24.491 W 122° 08.313

With geo markup: 

<div class="geo">
 <abbr class="latitude" title="37.408183">N 37° 24.491</abbr> 
 <abbr class="longitude" title="-122.13855">W 122° 08.313</abbr>
</div>

This geo might be displayed as:

N 37° 24.491 W 122° 08.313

Note that since the real world example used a more human readable presentation of the geo coordinates, we use the abbr-design-pattern to keep that more human readable presentation, and in addition provide the respective absolute numerical values for the geo.

Examples in the wild

This section is informative.

The following sites have published geos, outside their normal context of hCards, and thus are a great place to start for anyone looking for examples "in the wild" to try parsing, indexing, organizing etc., in addition to hCard examples in the wild. If you find geos outside of hCards anywhere else, feel free to add them to the top of this list. Once the list grows too big, we'll make a separate wiki page.

Implementations

This section is informative.

The following implementations have been developed which either generate or parse geos outside the context of hCards. If you have an geo implementation, feel free to add it to the top of this list. Once the list grows too big, we'll make a separate wiki page.

References

Normative References

Informative References

Work in progress

This specification is a work in progress. As additional aspects are discussed, understood, and written, they will be added.

Related Work

  • luna (proposal for geo-style microformat for co-ordinates on The Moon)
  • mars (proposal for geo-style microformat for co-ordinates on the planet Mars)
  • geo-extension-strawman - extends geo for representing coordinates on other planets, moons etc.

Similar Work

See Also

Related Pages

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