GeoRSS is a method of describing and pinpointing the physical locations of Internet content. Using GeoRSS, it is possible to search for Web sites or items based on relevant geographic locations. In addition, GeoRSS facilitates the immediate dissemination of RSS feeds to specific users based on event type and location. For example, during an outbreak of severe weather in Minnesota, all tornado-related alerts and warnings within 100 kilometers of a specified location such as postal ZIP code 55455 can be delivered to a user's computer, personal digital assistant (PDA), cellular telephone set or other digital communications device.
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GeoRSS makes use of Geography Markup Language (GML), a way of storing and transporting geographic data in Extensible Markup Language (XML). The original GML model was based on the Resource Description Framework (RDF) developed by the World Wide Web Consortium (W3C). GML retains many of the features of RDF including intelligent agents and a standard syntax for describing and querying data.
In GML, the characteristics of geographic objects are encoded as elements within documents. These elements can describe complex geographic features such as canyons, lakes and rivers. Humanmade creations such as buildings, parks and cities can also be described. In GML, locations are mathematically specified on the basis of geometric points, lines (also called line strings or line segments) or boundaries (also called polygons). This process is called geotagging.
In geotagging, a point is defined by an ordered pair in which the latitude coordinate is listed first, followed by a space and then the longitude coordinate. A line is defined by two points representing its ends. A boundary consists of three or more points defining a polygon on the earth's surface. The edges of a polygon can be lines of latitude and longitude, in which case it forms a four-sided figure called a box. Alternatively, each edge of a polygon edge may be a geodesic, which is a line representing the shortest distance between two points on the earth's surface. Upper and lower elevation limits can be defined for any boundary if three-dimensional data is needed.
From a user standpoint, locations can be less formally defined by means of geocoding, in which familiar features such as postal codes, street names, addresses, intersections or landmarks are assigned points, lines or boundaries.