Geography Markup Language (GML) 3.3 is now out for public comment. Not to say that this isn’t exciting on its own merits, but there’s an incredibly new feature in it — compact encodings! Clause 7 (page 16 in the PDF) has a great little section called “Compact Encodings of Commonly Used GML Geometries.” It finally defines a concise encoding for describing simple points, lines and polygons (and a few other shapes as well). For example, here’s a picture of the lineage of the new <SimplePolygon>, which compresses the old <Polygon> from 7 elements to 2.
In short, here are example points, lines and polygons that are now legal GML.
<Point> <posList>42.3 -71.9</posList> </Point>
<LineString> <posList>42.3 -71.9 42.4 -71.8</posList> </LineString>
<SimplePolygon> <posList>42.3 -71.9 42.5 -72.2 42.4 -72.1 42.4 -72.0</posList> </SimplePolygon>