SqlGeography is very picky about the order of points when reading Well Known Text (WKT): if your WKT points aren’t just so, the de-serialization will throw something like this:
A .NET Framework error occurred during execution of user-defined routine or aggregate "geography":
Microsoft.SqlServer.Types.GLArgumentException: 24205: The specified input does not represent a valid geography instance because it exceeds a single hemisphere. Each geography instance must fit inside a single hemisphere. A common reason for this error is that a polygon has the wrong ring orientation.
Luckily, there are smarter people in the world than me. Here’s a post on how to use T-SQL to ensure correct ring orientation. Here’s how I do it using Microsoft.SqlServer.Types in C#:
// a helper SqlGeometry, which isn't picky about ring orientation
var geometryHelper =
// STUnion will automagically correct any bad ring orientation
var validGeom =
// use the validGeom with correct ring orientation to
// create a SqlGeography.
var validGeography =