W3C Semantic Web Interest Group: Basic Geo (WGS84
lat/long) Vocabulary
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W3C Semantic Web Interest Group
Basic Geo (WGS84 lat/long) Vocabulary
Nearby in the Web:
ESW:GeoInfo wiki
del.icio.us/tag/geo
locative.us
Mapping Hacks
SchemaWeb entry
Editor:
Dan Brickley
danbri@danbri.org
> (SWIG Chair)
This is a
basic
RDF vocabulary that provides the
Semantic Web community with a namespace for representing
lat
(itude),
long
(itude) and
other information about spatially-located things, using WGS84 as
a reference datum.
The vocabulary is getting significant usage, both (as intended)
within RDF documents, but also as a namespace used within non-RDF XML
documents, such as RSS 2.0 (
see below
).
The
Locative
packets
format uses this vocabulary, as do Map Bureau's
RDF mapping
tools.
The
geocoder.us
site, provides a free
geocoding service for the US, based on TIGER data, and accessible via
an
RDF Web service
that uses this
vocabulary. Other applications include
blogmapper
and
openguides
. The
WordKit
system
also uses it for geocoding RSS 1.0 (ie. RDF), RSS 2.0 (non-RDF) and Atom
(non-RDF). The
Yahoo!
Maps
service also makes use of this namespace, although
apparently only within a RSS 2.0 context. See the
ESW:GeoInfo
Wiki
entry for links to other uses of this work.
Status of this Document
This document was created as an informal collaboration within
W3C's
Semantic Web Interest
Group
. This work is not currently on the W3C
recommendation
track
for standardization, and has not been subject to the
associated review process, quality assurance, etc. If there is
interest amongst the W3C membership in standards work on a
location/mapping RDF vocabulary, this current work may inform any
more formal efforts to follow.
Overview
This vocabulary begins an exploration of the
possibilities of representing mapping/location data in RDF, and
does not attempt to address many of the issues covered in the
professional GIS world, notably by the
Open Geospatial Consortium
(OGC). Instead, we provide just a few basic terms that can be used in RDF (eg.
RSS 1.0
or
FOAF
documents)
when there is a need to describe latitudes and longitudes. The
motivation for using RDF as a carrier for lat/long info is RDF's
capability for cross-domain data mixing. We can describe not only
maps, but the entities that are positioned on the map. And we can use
any relevant RDF vocabularies to do so, without the need for expensive
pre-coordination, or for changes to a centrally maintained schema.
Examples
A basic, standalone example:
An
example
that combines Geo,
Dublin Core
and
FOAF
vocabularies:
xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns="http://xmlns.com/foaf/0.1/">
An example (from
WorldKit
) of
geo-coding with RSS 1.0:
xmlns="http://purl.org/rss/1.0/">
...
http://example.com/geo
...
History
The origin of this workspace was the
2003-01-09 discussion
in the RDF Interest Group
IRC channel
. We are taking a similar
approach to the exploration of RDF vocabulary for calendars,
although that work is more mature. See the
RDF Calendar Workspace
for
more information.
Basic RDF Geo Vocabulary: Point/lat/long/alt
See the
SchemaWeb
site for an overview of classes and properties, or the
underlying RDFS/OWL
vocabulary description.
Currently we specify only a very minimalistic RDF vocabulary
for describing
Point
s with
lat
itude,
long
itude, and
alt
itude properties from the WGS84 reference
datum specification.
This design allows for basic information about points to be
described in RDF/XML, and augmented with more sophisticated or
application-specific metadata.
The vocabulary also defines a property
lat_long
, but this should probably be removed,
as few commentators have valued it.
The vocabulary defines a class 'Point', whose members are
points. Points can be described using the 'lat', 'long' and 'alt'
properties, as well as with other RDF properties defined
elsewhere. For example, we might use an externally defined
property such as 'bornNear' or 'withinFiveMilesFrom', or perhaps
other properties for representing lat/long/alt in non-WGS84
systems.
The 'lat' and 'long' properties take literal (ie. textual values),
each in decimal degrees. The 'alt' property is decimal metres about
local reference ellipsoid.
Design note: Datatyping and Whitespace
Whitespace in property values is insignificant, and
discouraged. We do not use RDF's datatyping mechanism in the
vocabulary's schema to note that the
rdfs:range
of
the
lat
long
and
alt
properties are XML Schema
float
datatypes. Instead,
from RDF's point of view, the properties are simply strings.
This reduces the syntactic burden on RDF/XML documents using
our vocabulary, since we write lat and long information as
strings. The string representation of lat and long should follow
the rules for XML Schema
float
, even though we do
not indicate explicitly in RDF that we are representing floating
point numbers. A future version of this document may be stricter
about whitespace when marking up
float
values, so it
is probably best to avoid any whitespace in your lat/long/alt
markup.
The semantics of the lat/long/alt properties are unaffected by
xml:lang values, if present.
Design note: non-RDF XML
While it is quite possible to use the namespace in non-RDF XML
documents, developers should note that this reduces the availability of
such data within the
Semantic Web
, since specialist knowledge
of each XML tagset is needed before data can be safely interpreted. The
GRDDL
specification offers an XSLT-based mechanism for mapping such data
into RDF.
Discussion
As this is an RDF vocabulary, we define properties of a kind
of thing, a Point, rather than the structure and characteristics
of an XML document type. XML Schemas and DTDs typically adopt the
latter approach, and thus provide more guarantees about the
information content of each document of some type. By contrast,
our RDF vocabulary provides no guarantee about which things will
be described in any particular RDF/XML document. For example, it
may turn out that many point descriptions omit the altitude
property, 'alt'. This doesn't make those documents
invalid
in any sense; they are merely less
informative.
We can note some rules for reasoning about the identity
conditions for points. If we encounter a description of a
Point
, call it ?X, and another, call it ?Y, and
?X and ?Y have identical values for their 'lat' and 'long' and
'alt' properties, we can conclude that ?X == ?Y, ie. that ?X and
?Y represent the self-same thing. Anything that has any 'lat',
'long' or 'alt' properties will be a 'Point'. In our RDF Schema
for the vocabulary, we indicate this using the rdfs:domain
property.
Point
has only one 'lat', only one 'long',
and only one 'alt'; we could use W3C's Web Ontology Language
(OWL) to express this. OWL allows us to note that these RDF
properties are 'functional properties'.
Documents
An
RDF
vocabulary for WGS84 latitude/longitude/altitude markup
(namespace uri:
2003-01-10 #rdfig links
, including test data
SWIG Basic Geo (WGS84 lat/long) Vocabulary
(this document)
Development Plans
Regarding the
vocabulary: it is pretty simple and should hopefully stay that
way, ie. short and simple enough to memorise and use. There may
be some need to extend it, based on deployment experience, test
cases etc. Time will tell.
Interested SWIG members meet occasionally in the
#swig
IRC channel on
FreeNode. The
IRC logs
and
weblogs
generally serve as
meeting records. At the time of writing, no meetings are
scheduled.
For related work and further discussion and collaboration, see
the
GeoInfo
entry
in the
ESW
Wiki
Contact:
Dan Brickley
danbri@danbri.org
$Id:
HEADER.html,v 1.38 2004/02/06 17:38:12 danbri Exp $
recent changes
$Log: Overview.html,v $
Revision 1.21 2006/02/01 22:14:46 danbri
added a parag noting decimal degrees for lat and long; decimal metres above ellipsoid for alt
Revision 1.20 2005/07/08 18:22:34 danbri
A few more introductory words.
Revision 1.19 2005/07/08 18:14:35 danbri
added links to rss1, dublincore, foaf pages
Revision 1.18 2005/07/08 18:01:08 danbri
s/rdfig/swig/ somewhere i missed
Revision 1.17 2005/07/08 17:59:11 danbri
trimmed
Revision 1.16 2005/07/08 17:55:54 danbri
more links
Revision 1.15 2005/07/08 17:45:30 danbri
added geocoder link
Revision 1.14 2005/07/08 17:44:41 danbri
added geocoder link
Revision 1.13 2005/07/08 17:19:35 danbri
markup bug
Revision 1.12 2005/07/08 17:18:25 danbri
noted that 2nd eg uses DC too
Revision 1.11 2005/07/08 17:17:08 danbri
CSS
Revision 1.10 2005/07/08 17:14:35 danbri
CSS
Revision 1.9 2005/07/08 17:11:56 danbri
CSS
Revision 1.8 2005/07/08 17:11:06 danbri
CSS
Revision 1.7 2005/07/08 17:05:26 danbri
more examples
Revision 1.6 2005/07/08 16:55:36 danbri
tidying text
Revision 1.5 2005/07/08 16:54:25 danbri
moved nonrdf later into doc
Revision 1.4 2005/07/08 16:51:59 danbri
markup fixes
Revision 1.3 2005/07/08 16:50:41 danbri
more text, discussion of non-rdf xml, and links to apps
Revision 1.2 2005/07/08 16:33:23 danbri
added more navigation
Revision 1.1 2005/07/08 16:25:23 danbri
new writeup
Revision 1.38 2004/02/06 17:38:12 danbri
Fixed a bad commit screwup
Revision 1.36 2003/12/14 02:23:14 danbri
anchored
Revision 1.35 2003/12/14 02:19:29 danbri
anchored
Revision 1.34 2003/04/03 00:30:01 danbri
removed related links; linked to Wiki instead
Revision 1.33 2003/02/19 00:40:10 danbri
removed SuckyCaps from Grub[Ss]treet (even if it is WikiBased :)
Revision 1.32 2003/01/11 19:02:23 danbri
Updated datatypes section, now that datatyping has been removed from the
schema.
Revision 1.31 2003/01/11 12:27:52 danbri
Added link to 2.2M Danish addresses.
Revision 1.30 2003/01/11 12:09:12 danbri
Added Sean Palmer's work on computing distances in RDF, and his infomesh-geo schema.
Revision 1.29 2003/01/11 12:03:33 danbri
Added link to Sean Palmer's 'geo' URN proposal.
Revision 1.28 2003/01/11 11:19:58 danbri
Revised the note re whitespace to mention use of RDF datatyping, and
to discourage use of whitespace. This should be re-organised to separate the
two issues. Also noted need for clearer advice on the whitespace issue.
Revision 1.27 2003/01/11 10:57:40 danbri
Added final '#' to namespace uriref in one place that I missed yesterday.
Revision 1.26 2003/01/11 01:23:25 danbri
Added DAML Geofile data.
Revision 1.25 2003/01/10 23:05:49 danbri
Changed to say: *An* RDF Geo vocab... (there will doubtless be others).
Revision 1.24 2003/01/10 22:52:40 danbri
Fixed a bug in the identity reasoning section ('alt' was ommitted from
the identity rules). Added a paragraph contrasting RDF and XML schema
systems.
Revision 1.23 2003/01/10 22:33:54 danbri
Added example snippet. Also Syndic8 Geo metadata maker.
Revision 1.22 2003/01/10 21:31:43 danbri
Swapped a couple of paragraphs around, fixed some markup bugs and added a comment
explaining the role of rdfs:domain.
Revision 1.21 2003/01/10 21:28:29 danbri
Re-organised the page, and added some more detailed description of the
Point/lat/long/alt design, mentioning identity rules for the Point class and
the possible use of OWL to clarify the design.
Revision 1.20 2003/01/10 19:53:43 danbri
Added DCMI Point Encoding Scheme.
Revision 1.19 2003/01/10 19:46:54 danbri
Adding final '#' to geo vocab namespace uriref, for consistency with schema.
Revision 1.18 2003/01/10 19:45:28 danbri
Added link to Syndic8 metadata spec.
Revision 1.17 2003/01/10 17:58:22 danbri
Added a link to GML 2.0, Simon Cox et al. for OGC., Feb 2001.
Revision 1.16 2003/01/10 17:50:22 danbri
Added Muxway links, from Joshua Schachter.
Revision 1.15 2003/01/10 17:45:20 danbri
Added @semantics link from Alberto.
Revision 1.14 2003/01/10 16:51:46 danbri
Added streetmap Perl module, and reference to xmethods.net web service
directory.
Revision 1.13 2003/01/10 16:43:03 danbri
Added GeoURL location/add yourself page, NVML and DCMI Box Encoding
Scheme.
Revision 1.12 2003/01/10 16:09:45 danbri
Added Spacenamespace sample data from Jo Walsh, and ptr to PostGIS docs.
Revision 1.11 2003/01/10 14:15:14 danbri
Noted that OSGB FAQ includes pointers to conversion code.
Revision 1.10 2003/01/10 14:13:05 danbri
Added Garmin, UK waypoints and OS links.
Revision 1.9 2003/01/10 12:50:21 danbri
added previous cvs history, so you can see how busy I've been...
revision 1.8
date: 2003/01/10 12:48:14; author: danbri; state: Exp; lines: +8 -1
added blogmapper and rdfmap links
revision 1.7
date: 2003/01/10 12:42:05; author: danbri; state: Exp; lines: +4 -1
added rdfmap
revision 1.6
date: 2003/01/10 12:37:16; author: danbri; state: Exp; lines: +27 -8
added Status info
revision 1.5
date: 2003/01/10 12:30:23; author: danbri; state: Exp; lines: +3 -1
added opengis consortium
revision 1.4
date: 2003/01/10 11:59:03; author: danbri; state: Exp; lines: +3 -2
fixed buglet in vocab, added more wgs links
revision 1.3
date: 2003/01/10 11:46:43; author: danbri; state: Exp; lines: +4 -4
added more links
revision 1.2
date: 2003/01/10 11:40:50; author: danbri; state: Exp; lines: +5 -5
added more links
revision 1.1
date: 2003/01/10 11:28:17; author: danbri; state: Exp;
first cut at contextual overview doc