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INTERNET-DRAFT                                     Vancouver Webpages
<draft-daviel-html-geo-tag-08.txt>                   October 30, 2007
Expires: May 2, 2008
Intended status: Standards Track

               Geographic registration of HTML documents

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   The list of current Internet-Drafts can be accessed at

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   This Internet-Draft will expire on April 1, 2008.


   This memo describes a method of registering HTML documents with a
   specific geographic location through means of embedded META tags.
   The content of the META tags gives the geographic position of the
   resource described by the HTML document in terms of Latitude,
   Longitude, and optionally Elevation in a simple, machine-readable
   manner.  This information may be used for automated resource
   discovery by means of an HTML indexing agent or search engine.  META
   tags giving a civic location of a resource are also described.

1.  Introduction

   Many resources described by HTML documents on the World-Wide-Web are

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   associated with a particular place on the Earth's surface.  While
   resource discovery on the Web has thus far focussed on document title
   and open-text keyword searching, in these cases it may be beneficial
   to facilitate geographic searching.  Examples of this kind of
   resource include pages describing restaurants, shipwrecks, retail
   stores etc. Consumers may use this information in order to select the
   closest facility, and in order to navigate towards a resource by
   road, on foot or by other means.

   Although some resources, such as restaurants, have a street address
   which may be mapped to geographic location by existing tools, other
   objects on the Web, such as a photograph of a mountain, may not.

   This draft describes a method of adding static location data to
   legacy HTML documents using a construct that is familiar to many HTML
   authors.  It is intended to be concise, unambiguous, simple to use
   and compatible with existing editing tools.  The intended use is to
   provide location data to Web robots that typically revisit pages
   every few weeks.

   It is anticipated that in many cases this location data will be added
   manually by persons unfamiliar with GIS terminology or metadata
   standards.  For this reason a minimal data set with few options is
   preferred over a more complex and extensible one.

   The method described in this draft is not intended to preempt
   existing or future metadata encapsulation schemes which may better
   serve the needs of a particular community, such as geographic
   information systems (GIS). Nor is it intended to preempt richer, more
   structured data encapsulations such as RDF or XML, which typically
   require software to generate correctly.

2.  Coordinate Systems

   Resource positions on the Earth's surface should be expressed in
   degrees North of Latitude, degrees East of Longitude as signed
   decimal numbers.

   Where the precision of the coordinates is such that the datum used is
   significant, typically more precise than one kilometre distance,
   positions should be converted to the WGS 84 datum [WGS84].
   Elevations, if given, should be in metres above datum.  Positions
   given by a GPS set [GPS] with datum set to "WGS 84" will in most
   cases be adequate, of the order of 15 metres accuracy in horizontal
   position and 25 metres in elevation.

   It should be noted that elevations referred to the WGS 84 geoid will
   in some areas differ appreciably from those measured with respect to

Daviel,Kaegi                                                    [Page 2]

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   local datum in coastal regions, which may be Mean High Water Springs,
   Mean Sea Level, Higher High Water or a similar reference level, and
   will differ substantially from "ground level".  Use of elevation is
   not recommended unless its value may be reliably determined.

3.  Implementation

   XHTML, HTML or WML markup should be added to the document in the form
   of a META statement.  This should be placed in the document head in
   accordance with the XHTML specification [XHTML].

   There are several possible GEO identifiers:
   The identifier "geo.position" is used for  Latitude, Longitude and
   optionally Elevation data.
   The identifier "geo.country" is used for the two-letter country code
   from ISO 3166 [ISO3166], e.g.  "US" (United States), "DE" (Germany).
   The identifiers "geo.a1", "geo.a2" etc. are used to define a civic
   address, as in RFC 4776 [RFC4776].

   For resources within the United States and Canada, the "geo.a1"
   identifier corresponds to and the common 2-character State/Province
   codes [STATES][PROVINCES], e.g. "BC" (British Columbia), "CA"

   To facilitate machine indexing, wherever possible a controlled list
   should be used for civic elements. For instance, ISO 3166-2
   [ISO3166-2] might be used for "geo.a1"

   Use of the numeric "geo.position" is generally recommended to ensure
   accurate indexing.  However, if the resource described is localized
   to a country or region, but not to a single point, the civic
   identifiers "geo.country", "geo.a1" etc. may be used alone without a
   corresponding "geo.position" identifier.

   It is the intention of this draft to provide a means to associate a
   single point with an XHTML, HTML or WML document.  Some consideration
   should be given to the choice of location when describing a resource,
   given that positioning mechanisms may provide an accuracy of the
   order of ten metres in horizontal position.  For instance, when
   describing a retail store or small business, it may be more
   meaningful to give the position of the street entrance rather than
   the position of the center of the property.

   Although the XHTML specification [XHTML] states that the name field
   is in general case-sensitive, these GEO tags should be recognized by

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   compliant agents regardless of case.  Coordinates should be ordered
   (Latitude ; Longitude) as for RFC 2426, RFC 2445 (vCard and iCal
   specifications) [ICAL][VCARD].  If elevation is given, coordinates
   should be ordered (Latitude ; Longitude ; Elevation).

3.1 Migration from earlier versions

   To migrate documents and applicaitons written against earlier
   versions of this draft, the following correspondences are noted:

   geo.position       geo.position
   geo.region         geo.country   (2 character region)
   geo.region         geo.country and geo.a1  (extended region XX-YYY)
   geo.placename      geo.lmk     (landmark or vanity address)

4. Examples

     <meta name="geo.position" content="48.54;-123.84;115" />

   describes a resource 115 metres above datum at position
   48.54 degrees North, 123.84 degrees West, while

     <meta name="geo.position" content="-10;60" />

   describes a resource at position 10 degrees South,
   60 degrees East.

     <meta name="geo.country" content="CA" />
     <meta name="geo.a1" content="ON" />
     <meta name="geo.a3" content="London" />

   describes a resource in London, Ontario, Canada,

     <meta name="geo.country" content="GB" />
     <meta name="geo.a1" "LND" />
     <meta name="geo.a3" content="London" />

   describes a resource in London, England (Great Britain).

5. Semantics

   Values for latitude and longitude shall be expressed as decimal
   fractions of degrees.  Whole degrees of latitude shall be represented
   by a decimal number ranging from 0 through 90.  Whole degrees of
   longitude shall be represented by a decimal number ranging from 0
   through 180.  When a decimal fraction of a degree is specified, it
   shall be separated from the whole number of degrees by a decimal

Daviel,Kaegi                                                    [Page 4]

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   point (the period character, ".").  Decimal fractions of a degree
   should be expressed to the precision available, with trailing zeroes
   being used as placeholders if required.  A decimal point is optional
   where the precision is less than one degree.  Some effort should be
   made to preserve the apparent precision when converting from another
   datum or representation, for example 41 degrees 13 minutes should be
   represented as 41.22 and not 41.21666, while 41 13' 11" may be
   represented as 41.2197.

   Latitudes north of the equator MAY be specified by a plus sign (+),
   or by the absence of a minus sign (-), preceding the designating
   degrees.  Latitudes south of the Equator MUST be designated by a
   minus sign (-) preceding the digits designating degrees.  Latitudes
   on the Equator MUST be designated by a latitude value of 0.

   Longitudes east of the prime meridian shall be specified by a plus
   sign (+), or by the absence of a minus sign (-), preceding the
   designating degrees.  Longitudes west of the prime meridian MUST be
   designated by a minus sign (-) preceding the digits designating
   degrees.  Longitudes on the prime meridian  MUST be designated by a
   longitude value of 0.  A point on the 180th meridian shall be taken
   as 180 degrees West, and shall include a minus sign.

   Any spatial address with a latitude of +90 (90) or -90 degrees will
   specify a position at the True North or True South Poles,
   respectively.  The component for longitude may have any legal value.

   The vertical coordinate (Elevation)  must be expressed in meters
   above WGS-84 (EGM96) datum.  Points having zero elevation must not
   have a negative sign.

5.1 Interpretation

   User agents should accept metadata written according to the HTML or
   XHTML specifications [HTML][XHTML].

   Whitespace within a position value shall be ignored.

   An interpreting agent shall internally mark position values either
   valid or invalid.  If a position is marked invalid, it shall not be
   used to index or qualify the containing document.

   A position having a Latitude greater than 90 degrees, or less than
   -90 degrees, shall be marked invalid.

Daviel,Kaegi                                                    [Page 5]

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   A position having a Longitude greater than 180 degrees, or less than
   -180 degrees, shall be marked invalid.

   Where a value is given for geo.country, and the latitude and
   longitude values given for geo.position fall outside the recognized
   boundaries of this region, the position may be marked invalid.  For
   example, if a country code of "US" is given for a location in the US
   mainland, the position may be marked invalid if the Latitude is
   negative or the Longitude is positive.

   No formal reliance shall be placed on the precision implicit in
   position data.  It is likely that few content providers are qualified
   to determine reliable precision or accuracy data, and may use
   position data from other sources which does not give the datum.

5.2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

6. Formal Syntax

   DIGIT = %x30-39   ; 0-9
   PLUS = %x2B       ; +
   MINUS = %x2D      ; -
   DECIMAL = %x2E    ; .
   SEMI = %x3B       ; ;
   CRLF = %x0D.%x0A  ; return, linefeed
   SP = %x20         ; space
   HTAB = %x09       ; tab
   WSP = SP / HTAB   ;
   LWSP = (WSP / CRLF WSP)  ; linear whitespace
   UCASE = %x41-5A   ; A-Z
   HYPHEN = %x2D     ; -
   USCORE = %x5F     ; _
   country = 2UCASE  ; 2-letter code from ISO3166
   TEXT = <any OCTET except CTLs, but including LWSP>
   placename = 1*TEXT
   delimiter =  SEMI

   latitude =   [ MINUS / PLUS ] 0*2DIGIT [ DECIMAL *DIGIT]
   longitude =  [ MINUS / PLUS ] 0*3DIGIT [ DECIMAL *DIGIT]
   elevation =  [ MINUS / PLUS ] 0*DIGIT [ DECIMAL *DIGIT]
   position = latitude <delimiter> longitude [ <delimiter> elevation ]

   geocivic = TEXT  ; civic address elements as per RFC 4776

Daviel,Kaegi                                                    [Page 6]

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   XHTML or WML syntax:
   <meta name="geo.position" content="<position>" />
   <meta name="geo.country" content="<country>" />
   <meta name="geo.<civic>" content="<TEXT>" />

   HTML (legacy) syntax:
   <meta name="geo.position" content="<position>">
   <meta name="geo.country" content="<country>">
   <meta name="geo.<civic>" content="<TEXT>">

7.  Applicability

   As stated in the introduction, certain HTML documents may be
   associated with a geographic position, while other documents are not.
   For proper use of the GEO tags as described in this draft, the
   resource described in an HTML document should be associated with a
   particular geographic location for the lifetime of the document.  The
   tags may thus be properly used to describe an object fixed on the
   surface of the earth (or more properly, fixed in position relative to
   the surface of the earth) such as a retail store, a mountain peak or
   a railway station.  They may not be used to describe a non-localized,
   moving, or intangible object such as a multinational company, river,
   aircraft or mathematical theory.

   The geographic position given is associated with the resource
   described by the HTML document, not with the physical location of the
   document [RFC1876], or the location of the company responsible for
   publishing or hosting the document.  Thus, in some cases the country
   code used in "geo.country" may differ from the country code forming
   part of the host address in the document URL.

   Since the position given is associated with the content of the
   document, not the author, publishing and document conversion tools
   should not cache position data or store it in a template.

   In cases where the object being described is an area, such as a lake
   or a building, the position of the object should not in general be
   given to greater precision than the width of the object.  If desired,
   features within the object may be described in another page and their
   position given with greater precision.  In the case of an object such
   as a place of business, where only one page exists, the position of
   the entrance may be given rather than the position of the centroid.

8.  Security Considerations

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   The intended use of GEO metadata as described in this draft raises no
   privacy issues beyond those associated with normal use of the Web.
   It is assumed that information present in public Web pages has been
   published in accordance with applicable privacy regulations and

   If the location data describes the position of a mobile Internet
   device, filters applicable to possible end recipients (typically, the
   public Internet) should be applied. The webserver in this case acts
   as a Location Recipient [RFC3693].

9.  Internationalization considerations

   HTML meta element content, including geo elements, is coded using the
   character set of the containing document, typically UTF-8 or

   Geo.country and geo.position tag content should contain only ASCII

10.1  Normative References

   [HTML]  Raggett, Le Hors, Jacobs, "HTML 4.01 Specification",
        http://www.w3.org/TR/1999/REC-html401-19991224, W3C, December

   [XHTML] W3C HTML Working Group,  "XHTML 1.0 The Extensible HyperText
   Markup Language (Second Edition)",
     http://www.w3.org/TR/2002/REC-xhtml1-20020801, W3C,
     26 January 2000, revised 1 August 2002

   [ISO3166]  International Organization For Standardization /
        Internationale De Normalisation (ISO), "Standard ISO
        3166-1:1997: Codes for the Representation of Names of
        Countries and their subdivisions -- Part 1: Country codes",

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
        Requirement Levels", BCP 14, RFC 2119, March 1997.

10.2 Informative References

   [RFC3693] Cuellar, Morris et al., "Geopriv Requirements", RFC 3693,
        February 2004

Daviel,Kaegi                                                    [Page 8]

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   [RFC1876]  Davis et al., "A Means for Expressing Location Information
        the Domain Name System", RFC 1876, January 1996

   [RFC4776] H. Schulzrinne, "Dynamic Host Configuration Protocol
   (DHCPv4 and DHCPv6) Option
        for Civic Addresses Configuration Information", RFC 4776,
   November 2006

   [ISO3166-2] International Organization For Standardization /
        Internationale De Normalisation (ISO), "Standard ISO
        3166-2:1998: Codes for the Representation of Names of Countries
        and their subdivisions -- Part 2: Country subdivision code",

   [GPS]  ARINC Research Corporation, "Navstar GPS Space Segment /
        Navigation User Interfaces", IRN-200C-002, September 1997

   [WGS84]  United States Department of Defense; DoD WGS-1984 - Its
        Definition and Relationships with Local Geodetic Systems;
        Washington, D.C.; 1985; Report AD-A188 815 DMA; 6127; 7-R-
        138-R; CV, KV;

   [ICAL]  Dawson & Stenerson, Internet Calendaring and Scheduling Core
        Object Specification (iCalendar), RFC 2445, November 1998

   [VCARD]  Dawson & Howes, vCard MIME Directory Profile, RFC 2426,
        September 1998

   [STATES]  United States Postal Service, Official Abbreviations -
        States and Possessions,

   [PROVINCES]  Canada Postal Guide, Province and Territory Symbols

11. Acknowledgments Rohan Mahy and Patrik Faltstrom of Cisco Systems,
   for semantics.

12.  Authors' Addresses

   Andrew Daviel, BSc.
   Vancouver Webpages, Box 357

Daviel,Kaegi                                                    [Page 9]

<draft-daviel-html-geo-tag-08.txt>           Oct 2007 (Expires May 2008)

   185-9040 Blundell Rd
   Richmond BC
   V6Y 1K3

   Tel. (604)-377-4796
   Fax. (604)-270-8285

   Felix A. Kaegi
   Dipl.Informatik Ing. ETH (M.Sc.)
   Friedensgasse 51
   CH-4056 Basel

   Phone +41 61 383 10 01
   Fax   +41 79 625 27 41
   skype felix_kaegi

Daviel,Kaegi                                                   [Page 10]

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15a.  IANA Considerations

   This document does not introduce any IANA considerations.

Daviel,Kaegi                                                   [Page 11]

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