AsGml (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns the Geography Markup Language (GML) representation of a geometry instance.
For more information on Geography Markup Language, see the following Open Geospatial Consortium Specification:OGC Specifications, Geography Markup Language.
Syntax
.AsGml ( )
Return Types
SQL Server return type: xml
CLR return type: SqlXml
Remarks
Examples
The following example creates a LineString instance and uses AsGML() to return the GML description of the instance.
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('LINESTRING(0 0, 0 1, 1 0)', 0)
SELECT @g.AsGml();
This method returns the description as a LineString instance.
<LineString xmlns="http://www.opengis.net/gml">
<posList>0 0 0 1 1 0</posList></LineString>