STGeometryN (geography Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns a specified geography element in a GeometryCollection or one of its subtypes. When STGeometryN() is used on a subtype of a GeometryCollection, such as MultiPoint or MultiLineString, this method returns the geography instance if called with N=1.
Syntax
.STGeometryN ( expression )
Arguments
expression
Is an int expression between 1 and the number of geography instances in the GeometryCollection.
Return Types
SQL Server return type: geography
CLR return type: SqlGeography
Remarks
This method returns null if the parameter is larger than the result of STNumGeometries() and will throw an ArgumentOutOfRangeException if the expression parameter is less than 1.
Examples
The following example creates a MultiPoint``geography instance and uses STGeometryN() to find the second geography instance of the GeometryCollection.
DECLARE @g geography;
SET @g = geography::STGeomFromText('MULTIPOINT(-122.360 47.656, -122.343 47.656)', 4326);
SELECT @g.STGeometryN(2).ToString();