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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
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This Internet-Draft will expire on April 1, 2008.
Abstract
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
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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"
(California)
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,
while
<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
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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.
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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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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
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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
guidelines.
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
ISO8859-1.
Geo.country and geo.position tag content should contain only ASCII
characters.
10.1 Normative References
[HTML] Raggett, Le Hors, Jacobs, "HTML 4.01 Specification",
http://www.w3.org/TR/1999/REC-html401-19991224, W3C, December
1999
[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 /
Organisation
Internationale De Normalisation (ISO), "Standard ISO
3166-1:1997: Codes for the Representation of Names of
Countries and their subdivisions -- Part 1: Country codes",
1997.
[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
http://www.ietf.org/rfc/rfc3693.txt
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[RFC1876] Davis et al., "A Means for Expressing Location Information
in
the Domain Name System", RFC 1876, January 1996
http://www.ietf.org/rfc/rfc1876.txt
[RFC4776] H. Schulzrinne, "Dynamic Host Configuration Protocol
(DHCPv4 and DHCPv6) Option
for Civic Addresses Configuration Information", RFC 4776,
November 2006
http://www.ietf.org/rfc4776.txt
[ISO3166-2] International Organization For Standardization /
Organisation
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",
1998.
[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
http://www.ietf.org/rfc/rfc2445.txt
[VCARD] Dawson & Howes, vCard MIME Directory Profile, RFC 2426,
September 1998
http://www.ietf.org/rfc/rfc2426.txt
[STATES] United States Postal Service, Official Abbreviations -
States and Possessions,
http://www.usps.gov/ncsc/lookups/abbr_state.txt
[PROVINCES] Canada Postal Guide, Province and Territory Symbols
http://www.canadapost.ca/tools/pg/manual/b03-e.asp
11. Acknowledgments Rohan Mahy and Patrik Faltstrom of Cisco Systems,
for semantics.
12. Authors' Addresses
Andrew Daviel, BSc.
Vancouver Webpages, Box 357
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185-9040 Blundell Rd
Richmond BC
V6Y 1K3
Canada
Tel. (604)-377-4796
Fax. (604)-270-8285
advax@triumf.ca
Felix A. Kaegi
Dipl.Informatik Ing. ETH (M.Sc.)
Friedensgasse 51
CH-4056 Basel
SWITZERLAND
Phone +41 61 383 10 01
Fax +41 79 625 27 41
skype felix_kaegi
felix.kaegi@gmail.com
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15a. IANA Considerations
This document does not introduce any IANA considerations.
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