GML-GeoRSS GML From http://georss.org/gml
Geography Markup Language (gml) is an XML grammar written in XML Schema for the modelling, transport, and storage of geographic information...GML provides a variety of kinds of objects for describing geography including features, coordinate reference systems, geometry, topology, time, units of measure and generalized values. A geographic feature is "an abstraction of a real world phenomenon; it is a geographic feature if it is associated with a location relative to the Earth?. So a digital representation of the real world can be thought of as a set of features.
Polygon:
<feed xmlns="http://www.w3.org/2005/Atom"
xmlns:georss="http://www.georss.org/georss"
xmlns:gml="http://www.opengis.net/gml">
<title>Dino's Mt. Washington trip</title>
<link href="http://www.myisp.com/dbv/"/>
<updated>2005-12-13T18:30:02Z</updated>
<author>
<name>Dino Bravo</name>
<email>dbv@example.org</email>
</author>
<id>http://www.myisp.com/dbv/</id>
<entry>
<georss:where>
<gml:Polygon>
<gml:exterior>
<gml:LinearRing>
<gml:posList>
45.256 -110.45 46.46 -109.48 43.84 -109.86 45.256 -110.45
</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</georss:where>
</entry>
</feed>