Trace: Geotagging

Geotagging

From GISWiki

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 placenames.

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.

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=xxxxx e.g. geo:lat=51.4989
geo:lon=yyyyy e.g. geo:lon=-0.1786

where xxxxx and yyyyy are the coordinates of latitude and longitude of the associated 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.

GeoTagging in hardware

GeoTagging can also be enabled in hardware tools; for example, some digital cameras have built-in GPS receivers, which can automatically add GeoTags to the Exif data embedded in the photos.