Geotagging

From Wikipedia, the free encyclopedia

Geotagging is the process of adding geographical identification metadata to various media such as photographs, video, websites, or RSS feeds and is a form of geospatial metadata. This data usually consists of latitude and longitude coordinates, though it can also include altitude, bearing, accuracy data, and place names.

Geotagging can help users find a wide variety of location-specific information. For instance, one can find images taken near a given location by entering latitude and longitude coordinates into a Geotagging-enabled image search engine. Geotagging-enabled information services can also potentially be used to find location-based news, websites, or other resources.^[1]

Less commonly this process has been called geocoding, although the latter term usually refers to the process of taking non-coordinate based geographical identifiers, such as a street address, and finding associated geographic coordinates (or vice versa for reverse geocoding).

Contents 1 Geotagging techniques 1.1 GPS-formats 2 Using geotagging 2.1 JPEG-photos 2.2 HTML-pages 2.2.1 ICBM-method 2.2.2 RDF-method 2.2.3 Microformat 2.2.4 Wikipedia 2.3 Geotagging in tag-based systems 2.4 Geoblogging 3 See also 4 References

[edit] Geotagging techniques

The base for geotagging is positions. The position will in almost every case, be derived from the global positioning system, and based on a latitude/longitude-coordinate system that presents each location on the earth in a coordinate spanning from 180° west through 180° east along the Equator and 90° north through 90° south along the prime meridian.

[edit] GPS-formats

GPS co-ordinates may be represented in text in a number of ways, with more or fewer decimals:

Template	Description	Example
[-]d.d, [-]d.d	Decimal degrees with negative numbers for South and West.	12.34, -98.76
d° m.m′ {N|S}, d° m.m′ {E|W}	Degrees and decimal minutes with N, S, E or W suffix for North, South, East, West	12° 34.56′ N, 98° 76.54′ E
{N|S} d° m.m′ {E|W} d° m.m′	Degrees and decimal minutes with N, S, E or W prefix for North, South, East, West	N 12° 34.56′, E 98° 76.54′
d° m' s" {N|S}, d° m' s" {E|W}	Degrees, minutes and decimal seconds with N, S, E or W suffix for North, South, East, West	12° 34' 56" N, 98° 76' 54" E
{N|S} d° m' s.s", {E|W} d° m' s.s"	Degrees, minutes and decimal seconds with N, S, E or W prefix for North, South, East, West	N 12° 34' 56", E 98° 76' 54"

[edit] Using geotagging

Geotagging works two ways: First it tells people rather precisely where the content of a given media is located, but on some media platforms (such as Google Earth) it also gives the reverse ability: Showing people relevant media to a given location.

[edit] JPEG-photos

With JPEG-photos the geotag-information is typically embedded in the metainformation (typically as EXIF-data or XMP-data. These data aren't visible in the picture itself but are read and written by special programs and most digital cameras and modern scanners. The format used is degrees with decimals, and plus/minus indicator and can be read in detail by many programs, i.e. the cross-platform freeware tool ExifTool. A interpreted readout for a photo would look like this:

GPS Latitude                    : 57 deg 38' 56.83" N
GPS Longitude                   : 10 deg 24' 26.79" W
GPS Position                    : 57 deg 38' 56.83" N, 10 deg 24' 26.79" W

While the more uninterpreted EXIF-data looks like this:

GPSLatitude                    : 57.64911
GPSLongitude                   : 10.40744
GPSPosition                    : 57.64911 10.40744

Or even more:

GPS information:
GPSVersionID:2.0.0.0
GPSLatitudeRef:N
GPSLatitude:57 38 56.83
GPSLongitudeRef - E
GPSLongitude - 10 24 26.79

[edit] HTML-pages

[edit] ICBM-method

The GeoURL^[2] standard requires the ICBM tag^[3]:

<meta name="ICBM" content="50.167958, -97.133185">

The similar Geo Tag format allows the addition of placename and region tags:

<meta name="geo.position" content="50.167958;-97.133185">
<meta name="geo.placename" content="Rockwood Rural Municipality, Manitoba, Canada">
<meta name="geo.region" content="ca-mb">

[edit] RDF-method

The RDF-method is defined by W3 Group and presents the information in RDF-tags^[4]:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#"> <geo:Point> <geo:lat>55.701</geo:lat> <geo:long>12.552</geo:long> </geo:Point> </rdf:RDF>

[edit] Microformat

The Geo microformat allows coordinates within HTML pages to be marked up in such a way that they can be "discovered" by software tools. Example:

<span class='geo'>
<span class='latitude'>50.167958</span>; 
<span class='longitude'>-97.133185</span>
</span>

which might display as:

50.167958; -97.133185

(and gives a live Geo microformat on this page).

A proposal has been developed^[5] to extend Geo to cover other bodies, such as Mars and the Moon.

An example is the Flickr photo-sharing Web site, which provides geographic data for any geocoded photo in all of the above-mentioned formats.

[edit] Wikipedia

On Wikipedia it is possible to include geotagged information in articles (and thus also images), using the template {{coord}}. In the top right corner, the inserted coordinates will then be presented, as a link on the Wikimedia Toolserver^[6], where one then has the ability to click further on to different geographic content on the Internet. For the article Råbjerg Mile it looks like this:

[edit] Geotagging in tag-based systems

No industry standards exist, however there are a variety of techniques for adding geographical identification metadata to an information resource. One convention, established by the website Geobloggers and used by more and more sites, e.g. photo sharing sites Panoramio and Flickr, and the social bookmarking site del.icio.us, enables content to be found via a location search. All sites allow users to add metadata to an information resource via a set of so-called machine-tags (see folksonomy).

geotagged
geo:lat=57.64911
geo:lon=10.40744

where latitude and longitude are the geographic coordinates of a particular location. These are expressed in decimal degrees in the WGS84 datum, which has become something of a default geodetic datum with the advent of GPS.^{[citation needed]}

Using three tags works within the constraint of having tags that can only be single 'words'. Identifying geotagged information resources on sites like Flickr and del.icio.us is done by searching for the 'geotagged' tag, since the tags beginning 'geo:lat=' and 'geo:lon=' are necessarily very variable.

A further convention proposed by FlickrFly adds tags to specify the suggested viewing angle and range when the geotagged location is viewed in Google Earth:

ge:head=225.00
ge:tilt=45.00
ge:range=560.00

These three tags would indicate that the camera is pointed heading 225° (south west), has a 45° tilt and is 560 metre from the subject.

Both Panoramio (which is focused on showing geotagged pictures of the world) and Flickr, has the generated and place a picture from JPEG-metadata coordinates (as described above).

[edit] Geoblogging

Geoblogging attaches specific geographic location information to blog entries via geotags. Searching a list of blogs and pictures tagged using geotag technology allows users to select areas of specific interest to them on interactive maps.^{[citation needed]}

The progression of GPS technology, along with the development of various online applications such as Flickr, has fueled the popularity of such tagged blogging,^{[citation needed]} and the combination of GPS Phones and GSM localization, has led to the moblogging, where blog posts are tagged with exact position of the user.

[edit] See also

• Auto-geotagging
• Geocaching
• Geocoding
• Geocoded photo (Geotagging methods)
• Geographic information system (GIS)
• Geolocation
• GeoRSS
• Global Positioning System (GPS)
• Moblog
• Supranet
• Tagging

[edit] References