GeoTagging

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Geotagging, sometimes referred to as Geocoding, is the process of adding geographical identification metadata to various media such as websites, RSS feeds, or images. This data usually consists of latitude and longitude coordinates, though it can also include altitude and place names.

Geocoding also refers to the process of taking non-coordinate based geographical identifiers, such as a postal address, and converting them into geographic coordinates.

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 a latitude and longtitude into a Geotagging-enabled image search engine. Geotagging-enabled information services can also potentially be used to find news, websites, or other resources.

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[edit] Geotagging in tag based systems

There exist a variety of techniques for adding geographical identification metadata to an information resource. One convention established by the website called GeoBloggers, encourages users to add tags to their Flickr images and del.icio.us bookmarks, enabling them to be found via a location search. Both Flickr and del.icio.us allow users to add metadata to an information resource via a set of tags, see folksonomy.

The convention established by GeoBloggers uses three tags to geotag an information resource:

  • geotagged
  • geo:lat=latitude e.g. geo:lat=51.4989
  • geo:lon=longitude e.g. geo:lon=-0.1786

where latitude and longitude are the geographic coordinates of a particular location. These are expressed in decimal degrees in the WGS84 coordinate system, which has become something of a default coordinate system with the advent of GPS.

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=xxxx e.g. ge:head=127.00, where xxxx is the view heading in decimal degrees (0-360) where zero is looking North.
  • ge:tilt=yyyy e.g. ge:tilt=60.00, where yyyy is the view tilt angle in decimal degrees, where 0 is looking straight down and 90 is looking horizontally from ground level.
  • ge:range=zzzz e.g. ge:range=560.00, where zzzz is the range of the viewpoint in metres from the marker location.

[edit] Web sites

Geotagging HTML web pages is done with meta tags. The GeoURL standard requires the ICBM tag:

<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] Microformat

The Geo microformat allows co-ordinates within web 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 is in hand [1] 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] See also

[edit] External links

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